Both main lining pieces have elastic pockets -- the inside back has a large but non-padded laptop-sized pocket, and the inside front has a pocket that gets sewn into three (or whatever you want).

Once these are done, then it's a matter of sewing the lining main pieces to the exterior main pieces wrong sides together, and then sewing the three pieces you're left with (front, back, and gusset) into a finished backpack.

I made a running stitch along the bottom without backstitching at either end, and then pulled the threads to match the gather along the top.

I sewed mine into three equal pockets.

Now we're making the laptop-sized pocket.

I also made binding for the raw seams where the zipper panel is sewn to the gusset.