Download the proper version of Audacity needed for your computer's operating system from the Audacity downloads page (see References).
Install Audacity from the program you just downloaded.
Open Audacity and go over its features. Note the familiar tape-deck-style buttons at the top: rewind, play, record, pause, stop and fast forward.
Download the appropriate LAME mp3 encoder for your operating system (see References).
Double-click the mp3 encoder program to install it, following the instructions in the setup program. Do not change the destination folder.
Note the destination folder. You will need this information the first time you convert a file to .mp3 format.
Select "export as mp3" to convert the entire .flac file to .mp3 format. Audacity will prompt you for the location of the LAME encoder file.
Select the LAME mp3 encoder file from the folder in Step 3 above. Click "Open," then "OK."
View the Audacity workspace to ensure the .flac conversion processes properly. If necessary, select "Export as mp3" once again, and choose a file name and destination when the "Save file as" prompt appears.
Note the audacity workspace window. The mp3 filename should be in place. Play the file to ensure it works properly.