Taken from the Japanese Wii Music site:

Ad Lib Performance
- Choose among 50 tunes, 60 instruments, and a selection of stages
- As you play alone, you can record 6 different instruments separately and mix them

Share clips with friends
- Record your performances
- Design an album cover for each record
- edit performances that you’ve received
- send to friends

Lesson mode: Basic Play
- Learn the fundamentals of the game
- practice with all instruments to become familiar with them

Re-arranging Lessons
- Learn to choose the appropriate instrument depending of the the type of song, as well as the basics of conducting a musical performance

Drum Lessons
- Use both hands (Wiimote + Nunchuk) and your feet (Balance Board) to learn how to play a drum set

Minigames
- Minigame 1 : Conduct a Classical Orchestra
- Minigame 2 : Connect the Handbells
- Minigame 3 : Test your Musical Sensitivity

Link