Step 4: Begin weaving
This weaving process is called 'weaving with three warps'. You'll be going around the outer cord with your working strand, under the center two cords(which you treat as one cord), and around the other outer cord.
You weave it back over the center two strands and around the outer, continuing this process, back and forth. Try not to leave too much slack as you go to keep the weave uniform. Every couple of weaves, push your work tight, up towards the starting buckle end.