This bag is knit in the round, which means that you'd be working with double-pointed needles (which happen to be my favorite, but a lot of people dislike them). If this is one of your first projects, you can certainly knit it flat and then seam up the side. Stockinette stitch is knit on the right side, purl on the wrong side, or all knit stitches when working in the round. K2tog means to knit two stitches at the same time, to decrease into one stitch. As for the k6, k16, my guess is that it has to do with the way the stitches are distributed on the needles, but that's only my theory and I'd have to knit the bag to be sure.
Amy has videos for all of the techniques used in this project in her video sections. I'm too lazy to link them, though, sorry.
I hand-sewed a tarot card pouch out of velvet and satin, and it holds my cards beautifully and keeps them protected. What a wonderful gift for your friend.