Open Audacity and start a new session by going to the "File" menu and selecting "New Project".
Click the "Generate" menu and select "Click track" from the drop down menu. This will bring up the click track option screen.
Choose the tempo at which you would like the click track to play. The default starting tempo for Audacity and most metronomes is 120 beats per minute. If you don't know how many beats per minute to make the click track for your song, play the click track first and play some of the music along with it. You will immediately be able to determine if it is too fast or too slow for the song.
Select the time signature that you would like your click track to play to. The standard time signature is 4/4 time, which means there are four beats in every measure. Other common time signatures include 3/4 time (waltzes) and 2/4 time (marching).
Select how many bars of click track you would like generate. Ideally, the click track should run through the whole song. It is better to make the click track longer than the song, rather than shorter. Any part of the click track that exceeds the music, can easily be deleted.
Select "OK" at the bottom of the option screen and your click track will be created. You can continue to record your music in Audacity if you like. Alternatively, you can bounce out the click track by selecting it and clicking "File" and "Export audio as WAV." Once the click track has been bounced out, you can bring it in to any audio recording software you would like to.