I don't have music studio 12 - I use music maker 16 but it should be similar to your program.

If I understand correctly you want to play a vita instrument and record what you play.

You will need to record vita as a midi track - either by drawing in the notes in the midi editor or by connecting a USB midi keyboard -  select it in program settings then arm the track for midi record- press the record button .... then play your keyboard. I just got an M audio midi keyboard controller and its much more fun than drawing notes in the editor.
let me know if this answers you question or if you need more help.