Okay, so first things first, decide how big you want your bag to be and cut it. I cut till the crotch, but i would suggest you cut a little higher than that cuz there's some weird shit going on there :P
Note: because the crotch area has extra seams and stuff, my sewing machine needle broke. Twice.

turn the bag inside out and sew the bottom bit. You know, so that stuff doesn't fall out and stuff :P
When you turn it inside out, you'll see that the bag has already taken it's form.

This bit is optional. I rounded the edges of my bag by sewing along the chalk line.
<---- like so. :D

It should look something like this.

now for the handles!
Take a strip of jeans from the leg and fold it in half, wrong sides together and sew it along the side. This looks kinda messy, but I didn't mind. It gave the bag some edge :P If you want, you could hem the sides first.
make two straps like these.

pick where you want your straps to be and pin them in place. Use the sewing machine to sew them to your bag. (Remember to make them SUPER strong!)

And tadaaa!! The finished bag! xD
cute, innit?
Embellish it to your liking. I preferred to leave mine plain :)