Chain stitch is a simple stitch to make and it can be used to join pieces and as a filling stitch.
To make it, come up through the fabric and then make a stitch that starts in the same place or very close to where you came up and comes out a short distance forward. Leave the needle in place while you wrap the thread around the needle as shown in the picture. Then pull through and ease the loop so it looks nice.
Continue to do this until you are done.
Here is a piece that features chain stitch as a filling stitch:
It looks good in multiple colors and in a single color.