How to tie a Carrick Bend
Take the end of a length of rope and cross it over itself to make a crossing turn. Take the end (working end) of a second piece of rope (green) so that it lies across the crossing turn.
Take a second rope and make the crossing turn in the same way by first putting the working end through the first turn. Then lay the second rope over the first turn and take it under itself. Make sure the end of the second turn is lays on top of the standing part of the first turn.
Take the second end (green) under the crossing turn and then across the top of itself. Then tuck it underneath the crossing turn of the first rope.
It should now look like the picture shown here. Pull on all four ends to tighten the knot.
Ensure the knot is tight although the Carrick Bend does a good job by itself if you simply put strain on the ends of the rope. It collapses in on itself and becomes secure.