This isn’t the best DIY example because I’m extremely new to audacity and very new to audio mixing in general. There are a few basic things here that I think will be helpful though.
In order to mix 2 songs together, first load your 2 separate songs into audacity (I just drag them from my music folder.
Listen to each song to figure out which parts of each that you would like to use. For any mash-up song, you’re going to need and intro, so for this simple version I suggest choosing the intro from either of the existing songs, rather than mixing intros together. You can listen to one song at a time by muting one track.
Now you’re going to want to get rid of the intro from the track that you did not choose, which can be done by using the Selection tool to select the exact piece of sound you wish to delete, then pressing “CTRL-X”.
*Note: Audacity will not allow you to cut/copy/paste extra if the pause or play button is selected, you must select stop first.
Once that piece of sound is gone, you will find that the two tracks start at the same time, regardless of the missing intro. To remedy this, you must add silence for the track that is missing the intro so that your tracks come together at the right moment. This can be done in two ways- either by generating silence or using a Time-Shift.
Use the generate toolbar and select “Silence”. Then, in the Silence Generator box enter the length of the existing intro to compensate for the time. (The length/duration of your selection is always shown at the bottom of your screen. This is not as easy as the time shift, but may be the best option if you are switching between tracks in the middle of a song.)
A time shift is just as easy as making sure the “multi-tool” button is selected and dragging the track lacking an intro to line up with the end intro in the opposite track.
You can fine tune this transition by using the envelope tool to create a fade in/out and adjusting the volume. The song should now have the intro replaced.