Meshes are made up of Vertices, Edges, and Faces. Vertices (Vertex for singular) are also called Points, and you can think of them as the corners of a mesh. Each corner of a cube is one vertex. Edges connect pairs of vertices together. The edges of a cube are, well, the edges. Faces are made up of at least 3 edges. The sides of a cube are the faces. 3D modeling is all about manipulating the points and faces to make recognizable shapes.

To edit meshes, we need to go into Edit Mode. This is done by pressing Tab while in the 3D viewport, or by selecting it from the Object Interaction Mode dropdown in the upper left corner of the 3D viewport. 

In edit mode, you can switch between manipulating the vertices, edges, and faces whenever you want. Choose the option you want in the Select Mode buttons at the upper left of the 3D viewport, right next to the Object Interaction Mode dropdown. You can also switch between the modes with the number keys 1, 2, and 3.

Starting with vertex selection mode, try selecting a vertex. This works the same as in the default Object mode. You can click on a vertex to select it, hold shift and click to select multiple all at once, and all of the transformations in Object mode still work here. Try moving a vertex around with G (or the Move tool in the toolbar) and see that you can easily change the shape of the cube like this.

Editing edges and faces works the same way. Click an edge or face to select it, Shift+Click to select multiple, and you can manipulate any selected edges or faces all at once. If you select all the points or edges that make up a face, you will have that face selected when you switch into face selection mode.

Try messing around with the cube, or adding a different primitive and messing with that. It’s good to get comfortable with moving around vertices, edges, and faces, as you will be doing that a lot. I also highly recommend using the keyboard shortcuts as they will seriously speed up your work.

Now that you’re comfortable with transforming vertices, edges, and faces, it’s time to start adding more geometry to this cube. (If your cube is messed up beyond repair, no worries! Just go back to Object mode with Tab, move the cube to the side or delete it using X, and add a new cube with Shift+A or the Add menu.) Go into Face selection mode (either by clicking it in the upper left corner, or by pressing 3 on the keyboard) and select one face. We are going to extrude this face to make the cube longer. 

The Extrude tool is accessed by either pressing E with a face selected (or all the points or edges that make up a face selected) or by choosing the Extrude Region tool in the toolbar. When you extrude a face, new geometry is generated that connects to the previously selected geometry.

If you use the keyboard shortcut, the new geometry will slide with the mouse in the same direction as the face is pointing, and the position of the geometry is confirmed when you left click.

If you use the tool, you left click and drag to move the new geometry, and the position will be confirmed when you release your left click. You can also right click while positioning the geometry to snap it back to the original location.

The Inset tool will inset the selected faces similar to what you would get by extruding and then scaling down a face. It is usually used to make small indentations in objects. The tool is accessed in the toolbar, as you might expect, and the keyboard shortcut is to press I with at least one face selected. While using the tool, select one or more faces and then drag in on the circle that appears. For the keyboard shortcut, simply press I and then move the mouse to scale the inset.

When you have multiple faces selected for an inset, if they are touching each other they will all be treated as one big face. There is, however, a way to inset them all as individual faces. If you're using the tool, once you release it a menu will appear in the lower left hand corner. In there is a checkbox labeled "Individual." Checking that box will turn the inset into an individual inset, and if you want to modify the scale of the inset you can use the "Thickness" slider. If you're using the keyboard shortcut, simply press I a second time to switch to individual insets.

The Bevel tool is commonly used to round off sharp edges on models. 

To bevel, first select at least one edge. If you are using the tool from the toolbar, drag out on the yellow dot that appears. Release when you are happy with the amount that has been beveled. The keyboard shortcut for this is Ctrl+B.

After beveling with either the gizmo or the keyboard shortcut, a small dropdown box will appear in the lower left corner of the viewport. If you open up that box, you can change settings for the bevel operation.  The most important setting here is the Segments box. Turning up this value will make the bevel much smoother, although it will add more geometry to the object. This isn't really something to worry about now, but in the long run having too much geometry can be an issue. 

While using the keyboard shortcut, you can also scroll up and down on the scroll wheel to increase the number of segments.

The Loop Cut and Slide tool isn't immediately as intuitive as other tools, but it's one of the most useful editing tools in Blender. It lets you add a ring of edges, called an Edge Loop to your geometry. The ring will follow the quad geometry of the objects, which is a bit technical for this starting tutorial but for now you just need to know that edge loops only work on 4-sided geometry.

To add an edge loop, there is of course a tool in the toolbar and a keyboard shortcut. When using the tool, hover over any 4-sided face and you will see a preview line appear. Click to confirm placement, or click and hold to be able to slide it on the face. You can adjust the number of loop cuts as well as the position on the face in the box that appears in the lower left corner. 

The keyboard shortcut is Ctrl+R. After using the shortcut, you can adjust the number of cuts by scrolling. After clicking, you can move your mouse around to slide the position of the loop cut, and click to confirm it. Alternatively, you can right click to leave the position at the center.

To put these tools into practice, we're going to model a chair.

Making a chair in Blender is surprisingly simple, but it will use all the tools we just covered.

To start the chair, begin with a cube. If you've edited the existing cube, you can just delete it with X and then add a new one by pressing Shift+A and selecting Mesh->Cube. 

With the new cube added, go into edit mode and select everything. This can be done by hand, holding shift and clicking every point, but there is also a keyboard shortcut for selecting everything: pressing "A" will select all items. (as a side note, using Ctrl+A in a lot of programs will select all items - try it in your file explorer or in a text document!) 

With everything selected, scale down on the Z axis to make the seat of the chair. Try and get it to a thickness you're happy with, but it can be adjusted after the fact as well.

Next, we will add edge loops to create faces for each of the chair legs. The goal here is to create even squares on each corner of the cube, so that we can extrude them down for the legs. To do this, add an edge loop and slide it closer to one side, so that the distance between the edge loop and the side of the cube is about the width you want the chair legs to be. Repeat this on the other side, and then repeat in the other direction. 

If you hold down Shift while sliding the edge loops, you can move with more precision. 

Now, we're going to make the legs of the chair. This is done through an inset and an extrude operation. Select the faces on the corners of the underside of the chair. To make sure you're on the underside of the chair, you can look at the Navigator Gizmo and check that the Z icon is on the top of the circle. With the four faces selected, inset them all a little bit and then extrude them down. If you're not happy with the length of the legs, you can move the bottom faces up or down to change it.

Now to add the back of the chair, we're going to use another extrude. Select a line of faces on one edge of the chair - since the model is currently symmetrical from all sides, it doesn't matter which you choose. With a line of faces selected, extrude it up. The chair is almost done now!

To round off the top of the chair, we're going to use a bevel. In edge select mode, select the corners of the chair back. Then, bevel them. While doing this, you might realize that bevels can't go past other edges. If this is a problem, select the edges in the middle and move them inwards. You can round the bevels out by either scrolling up while using the keyboard shortcut, or by adjusting in the popup menu that appears in the lower left. 

With that, the chair is done! Make sure you save this file, as we're going to texture this model next. For some other modeling practice, you could try modeling a table to go along with the chair. Below, I'll put a GIF showing the process of making a small table, using the same techniques as before.