The verb accompany means to keep someone company, or to be their companion on a trip or journey. In a musical sense, accompany means to play background music for the lead singer or soloist.
If you want your friend to keep you company on your way to the store, you could ask her to accompany you on the walk. Or, if you want your friend to play piano while you sing a song, you could ask her to accompany you on piano. Just don’t ask her to do both at the same time or your friend may not want to accompany you anywhere any longer.