You put the girth straps through them. The straps that are under the saddle flap. LOL, im really tired so the name escapes me. Its another way to hold the saddle pad in place if you can't get the girth through the strap on the bottom.
Hope that made sense....
The girth goes through the bottom one, and then the you put the billets through the other one (Usually you can either just stick them through or you can velcro around them and pull the buckle gaurd down. I realize that maybe makes no sense... Let me see if I can find any better pictures.
Those are the billet straps. Billets are the leather pieces your girth buckles on too. The straps go on the first billet before you put your girth on. Also, if you have a buckle guard, the billet straps should go above the buckle guard.
The are used to help keep the saddle pad in place. I use them because my saddle pads always seem to shift :P.
I zoomed in on one of my pictures; I hope this helps a bit. You can kind of see the two straps...You hook the velcro onto the first billet strap. (there are two in this picture, one for my saddle pad, one for my half pad)
Nice pictures. I just wanted to point out (in case someone gets confused), that in the second picture there is an extra leather strap. The strap is either that of a breastcollar/martingale, or side reins. Please correct me if Im wrong.
:) I like the easily visible billet strap and buckle guard. They help my previous explanation make sense. Haha