Back stitch is the first stitch I teach in all my embroidery workshops. It's the foundation for many other stitches and great for any type of outlining. Chances are, if you've done any kind of hand sewing before, you've done back stitch.
Here's how ya do it:
Bring needle up at A and re-insert at B (photo one). Pull all the way through to the back.
Bring needle up at point C, and back down at A (photo two). Pull all the way through to the back.
Bring needle back up at D and back down at C (photo three).
Repeat as necessary.