Yes, you should use the breather button, that's what it's there for. The bellows action changes for each tune, so as you learn how to play a tune (right hand fingering, left hand direction of the bellows) you'll also be learning just how much air is needed.
As a beginner, only use the button as needed and don't ride it. In other words, open it fully when needed but don't slightly squeeze it when playing. That was what John Williams told me several years ago. In the next breath, he said that there are times when riding the air button might be appropriate. You need to learn more about the tunes you're playing as welll as your own box before you get into habits that might make for sloppy playing. You can break the rules later . . .
