You'll need the owners manual to be sure. On some 4 tracks there's a sequence of steps you have to take... ie, setting which tracks to play and which to record, assigning which bus the signal is routed, setting the levels.
It's an art in itself and too involved to explain here.
You really need the manual for your machine so you can go through the process step by step and then do it several times until you get used to it.