First, thread your needle and tie a knot. Stitch through the back and secure the knot near the edge of your piece.
Now, thread on 3 beads to start. Make a little stitch through the front of the fabric about 1/8-1/4 in from where your thread started. This distance will vary based on how large your beads are. You want the beads to make a nice little loop and not be stretched too far.
Now come up from the back and go back through bead #3. You will have stitched through bead #3 twice now and your thread will be coming out through that bead.
Add 2 beads and repeat: make a stitch through the front of the fabric, come back up through bead #3 etc.
You can change colors if you like and make your edging look a little different by making bead A be something and bead B something else.