So first I cut out all my pieces. I ended up with some scraps, which I made into pockets... You can do pockets wherever you want... or not at all... but things tend to get lost in the bottom of backpacks, so I would recommend some pockets.
I started with the exterior back. I padded it with the batting to make it more comfortable, and to give the backpack some structure. In order to hold the batting in place I sewed an "S"... the first initial of the little girl this backpack is for. You could do crisscross lines... whatever you want.
Then I sewed the pocket onto the front. I basically just took two scraps that were the same size and sewed them (right sides together) left a little space so I could turn them right side out and then sewed around three sides. (this way the inside of the pocket looks finished too.)
Now next I would recommend sewing the straps. I did not take pictures of this process... sorry. just do right sides together with the batting on top of one of the "wrong sides" sew down both sides. then turn right side out. the batting should end up between the two layers of fabric. Then sew a straight line down the middle. I measured an existing backpack's straps with the person I was making it for wearing it... to ensure the proper length... You could also make the straps wider if you wanted to.
now the sides were the trickiest part for me. I simply pinned the long strip at each end, then eyeballed the middle of the strip and the middle of the backpack... then I pinned it. I continued to do that all the way down. You have to repeat the process for both sides of each strip. I didn't really worry about making mine line up perfectly, but it did kind of work itself out. Then I sewed on the bottom. DON"T FORGE TO PUT IN YOUR STRAPS!!! The corners are a little messy, but you are never going to see that because it will be on the inside, so don't stress it.
I sewed the lining the exact same way, just straight sides, instead of gathered.
Sew right sides together on the top flap also, leaving the flat side open. Insert one side of the magnetic closure, then sew the top flap to the top back of the backpack. DON'T FORGET THE STRAPS AND THE HANGING STRAP!!
Next I took a piece of scrap fabric and sewed it on the front in the middle about 2" from the top edge. Then I made two button holes in it. Then I sewed a long piece of fabric (for tying it shut) onto the seam that connects the side to the back. (I did this on both sides.) parallel with the button holes. I brought the strings around and put them through the button holes. Then I sewed the lining to the backpack around the top (right sides together) leaving a gap to turn it all right side out. Then I did a straight stitch all the way around the top to secure it and close the gap.
I am so not the best at tutorials... sorry, but if you have any sewing skills whatsoever, you can definitely make this... it is not hard... but it is a little time consuming. =) happy crafting!