Go to https://www.audacityteam.org/download/. Per your operating system, click the corresponding download link and follow the relevant installation instructions. Windows users will be given the option to download the software as an .exe installer or a ZIP archive; the former is preferable for easy installation.

By this point you should have the latest version of Audacity installed on your computer. Opening the program, your window should look something like Fig. 1, minus my marks.

Audacity, like most other audio (and video) editing platforms, is organized around “tracks,” which represent layers of sound. If you were producing a song in Audacity, you might have separate tracks for each instrument: one for the drum kit, another for guitar, vocals, etc. To add a new track, drag an audio file of any format into the dark blue space, as shown above. 

Fig. 1 The anatomy of the Audacity UI. 

(1) Toolbar, containing from left to right and down: a selector tool, an “envelope” tool to modify the volume of tracks, a draw tool to modify individual samples in a clip (advanced), a zoom tool, a “time shift” tool to move highlighted clips around, and a multitool. 
(2) Audio input selector. If you’re recording new audio in Audacity, make sure you select here the microphone you plan to use!
(3) Record button
(4) Audio playback selector. Here, select which audio device connected to your computer you’d like Audacity to play sound on. 
(5) Effect tab. This contains an array of tools and effects that can be applied to individual tracks or a project as a whole.
 

Let’s say you’re editing a podcast, and want to cut together a series of tracks recorded at various times into a single, seamless montage. This might involve (a) trimming unimportant bits from each track, (b) cutting a track into multiple pieces, and moving each piece around, and (c) arranging each of track so that one follows right after the other.

(a) First, trimming: click on the selector tool (Fig. 1(1)). With your cursor, left-click and drag over the area on your track you’d like to remove. Upon doing this, the area you selected should be highlighted in purple. If you’d like to modify the area you have selected, mouse over either edge of your selection until your cursor becomes a hand pointing either left or right; drag the selection to your preference. To remove the area you have selected, press delete. (for Windows users, backspace works also) Your selection should now have disappeared.

(b) As with (a), use the selector tool to specify which area of your track you’d like to excise and move around. However, once selected, press either command + x (MacOS) or ctrl + x (Windows) instead of delete. Then click on the grey workspace and press command/ctrl + v. Your selection should appear in a separate track below the one you had selected. 

To move each track, click on the time shift tool. Click on the track you’d like to move and drag it about the workspace to your preference. Note that this moves all the clips you have placed in a given track; if you’d like to move a particular clip without moving others, you’ll have to place it in a new track!

(c) With the time shift tool, drag one track such that its start butts-up against another track’s end (or its end against the other track’s start). You’ll notice that a yellow line will appear once the tracks become sufficiently close, and the two tracks will lock into precise, sequential position; this indicates that one track will play immediately after the other. 

Let’s try editing a track such that it crescendos at its start and decrescendos at its end. Click on the envelope tool. Purple bars should appear above and below each track.

Like many other audio editing softwares, increases or decreases in volume in Audacity are represented graphically by “nodes” -- points at which the Think of each node like points on a line graph: if one node “spikes” above or below its neighbor, this indicates a rapid increase or decrease in volume. On the other hand, one node gradually sloping into another indicates a slow increase or decrease in volume.

To create a new node, click on a track. You’ll see a white dot appears where you click: this a node. 

Then, click on another point later on in your track. Another node will appear. To create a crescendo between the first and the second nodes, drag the second node up. To create a decrescendo between the first and second nodes, drag the second node down. 

You’ll see below that I’ve created four nodes in total: two for the beginning and end of the crescendo at the beginning of the track, and two for the beginning and end of the decrescendo at the end of the track.