I had tried my best to make a simple tutorial for you..
This is what your outside bag should look like at this point.
For the inside POCKET you will need:
Sew 3 sides of the pockets (leave the top open) after you first top stitching both of the pocket shape fabrics.
Turn right side out. Place the pocket in the middle of the lining.
Sew close to folded edge on strap, top-stitch 1/4" in from outer edge stitching.
Place lining fabric inside the outside fabric right sides together.Pins straps and top edge of bag well.
Turn the bag right side out by pulling outer shell through the opening in the bottom side of the lining.
If you are happy with everything, finnish by top stitching a 1/4" from the edge all around the top of the bag.