First, you need to measure each of the panels of your bag. They will vary since crochet is not an exact science. Add about 1/2 inch to each of the measurements to give yourself plenty of room for seam allowances.
Cut 2 large side panels (mine were 10 x 14 inches).
Cut 2 short side panels (mine were 10 x 5 inches).
Cut 1 bottom panel (mine was 5 x 14 inches).
Sew them together. I sew down the length of each of the sides first, which creates sort of a tube. I also do a zigzag stitch over the raw edges. Then, I sew the bottom on. (I didn't bother taking a lot of pictures since it is black fabric and black thread.) I match up the long length of the bottom panel with the right side of the bottom of the tube. I sew from approximately 1/4 inch in to the opposite side, at about 1/4 inch in, backstitching on each side. I repeat this process for the other long length. Then, I sewed the short sides together, sewing over the openings left in the corners and backstitching. I zigzagged around all of these raw edges.
It produces this bag shape.
Place this liner inside the bag.
Fold down the top edge and pin it, matching with the top edge of the crochet bag. Try not to stretch the crochet too much, as the fabric will not stretch as far as the yarn will.
Set your stitch length to a longer stitch. I used 4.5. Sew around the top edge of the bag, crochet side UP! Backstitch at the beginning and end. All done!
Now you have a fun, funky, fully lined crochet granny square bag!