You drag it to an audio track. (Hold down the Ctrl key as you add it to override the "ripple" effect.)
For best results, use WAV files.
Welcome to the forum.
First, I would record, or produce my musical composition to end up with a PCM/WAV file @ 48KHz 16-bit.
Then, just Import that (Get Media), to bring it into the Project. Click on it, in the Project Panel, and drag it to the Timeline, into an empty Audio Track. As some users have had issues with the Fixed Audio Track, Soundtrack, I would just choose an empty one. Done.
PS - I would not use MP3, or any heavily-compressed Audio format/CODEC.