Chain stitch is a basic line stitch. It can also be used as filling as well. Experiment and have some fun with it!
Bring the needle up and pick up a small amount of fabric with the needle. Wrap the thread around the needle before you pull it through.
Pick up another small bit of fabric like before and wrap the thread around the needle.
Repeat as long as you like. Then just bring the needle to the back at the end of the last loop.