...going from sketch to song...
1. Record a sketch of your song. The sketch does not have to be of high quality, but care should be taken to make sure your music is in sync with the metronome. Otherwise, it will be difficult to provide a solid drum track for your song.
2. Record the click track.
3. Create a mix down of the sketch with your existing tracks on the left side and the click track on the right.
4. Convert the sketch to MP3 format - Wave files are unnecessarily large.
NOTE: the conversion will not cause sync problems.