Ladder braids are a decorative braid where the middle strand remains fixed in position. They were used for borders around other types of rugs (especially hooked rugs), but more for other decorations. Ladder braids are unique in that the center strand can be used as a 'drawstring' to shorten or shape the braid around corners or curves. Ladder braids can also be made with four and eight strands. 

Secure the six strands so that the strand that will remain in a fixed position is in the number 3 slot as show (bottom, center). 
Take the strand at the right edge (in the No.6 position): over 1, under 1, over 1 and hold it in the new position. 
Take the strand at the left edge (in the No. 1 position): under 1, over 1, under 1 and hold it in the new position.
Repeat, working the right and left strands alternately.