train someone on something
to educate someone in the use of something. We trained him on the high diving board, but he isn't ready for competition yet. She trained herself on the computer so she could write a book.
train something on (someone, something, or an animal)
to aim something at someone, something, or an animal. Dave trained the spotlight on Fred, who was just coming out of the building. Train your lens on that bush. There is a deer back there.