Making mittens

I am pretty much a beginner. I am trying to make a pair of mittens (one at a time of course). When you are in the part where you begin shaping the thumb, are you supposed to continue knitting all the way across or do you separate the rest of the mitten to be picked up again later?

Usually you start the thumb ‘gusset’ where it gets larger each round (knitting all the mitten stitches). When you have all the thumb stitches you need, you usually put those on a scrap piece of yarn and finish the hand. Then you go back and finish the thumb.