Place double fold bias right side down. Any bias tape should have one side slightly smaller than the other side. Take the smaller side and match the edge to the edge of the fabric strip as shown below. Use lots of pins.
Run a straight stitch line right on top of the fold in the small side.
Flip the bias towards the raw edges of the fabric strip (to the right in this particular case).
Flip the fabric to the right side and fold bias back to its original shape. This way the longer side of the bias will be enclosing the raw edges into the bias tape.
Make sure the longer side of the bias completely covers the line of stitches you've sewn onto the other side. Use lots of pins to keep bias and fabric strip together.
Edge stitch along the open edge (as close to the edge as possible, making sure this second line of stitches completely catches the previous line of stitches).