Knitting question

So I self taught myself by arm knitting a scarf. I also made headbands with needles. But I want to make a throw blanket. So my needles are large. Idk what size. It says 13 on the end. And they’re like twelve inches long. Do I need to keep all of the stitches on the needles or can I slip them off the end and put them back when I need them? Also how many stitches to I start with. I just want a throw blanket. I would like to make one for Christmas. I know I’ll take forever and I want to start it now. I know I kind of sound stupid but I’m not good at reading directions