Making a crochet chain can be quite simple. I love using them when I want a simple cord and don't want to knit one.
Tie a slipknot at the beginning of the yarn strand.
Place the loop onto the crochet hook. Insert the hook through the loop and under the longer yarn.
Wrap the yarn once over the hook and in front of the loop. Also known as the "thread over".
Pull the new loop through first loop on the hook. This makes one chain (ch).
Repeat until the chain becomes the desired length. You are creating chain stitches, abbreviated as 'ch sts'. One loop should always remain on the crochet hook. Continue until desired length is achieved one loop should always remain on the crochet hook. Always keep your thumb and forefinger near the stitch on which your working, to ensure steadiness and good control as per photo.
Cut yarn and pull through the loop to fasten off.
Adapted from, How to crochet a chain from http://www.wikihow.com/Crochet-a-Chain