The method I used on the Super Waves Market bag is a type of chained cast on. It is made with a typical crochet foundation chain, picking up stitches on both sides of the chain.
First, chain the number of stitches the pattern requires. It should look like a braid.
With the loop from last chain still on hook, pull up a loop in the next and each stitch down one side of the chain (make sure they are all on the same side of the chain)
Your stitches should look like this:
Turning your work, pull your needle up and out of the stitches, leaving them on the cable, and pulling a loop up through the other side of the same stitch, making two stitches in the same loop but on opposing sides. (If you look at the picture above you can see where the loops are on the bottom underneath the needle. Those loops are where you pick up your live yarn.)
Your stitches, as they are being picked up will look like this, if done correctly.
When all stitches are picked up, your work should have half of your stitches on the resting cable of the needle, and the others on the needle. To work in a round, place a marker at the end of the second row of picked up stitches, and you are now ready to work the next row.
If you have any questions let me know, and I will do my best to clarify things!