Ladderlock buckles with webbing straps are extremely handy on board any boat. Unfortunately, the proper threading technique is not obvious. There is a photo below which should help somewhat.

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We have stapled the webbing in place loosely to indicate how it should be threaded. The webbing loop on the left should be sewn in place permanently. The loop on the right is used to adjust the length of the strap. Note that the webbing comes up from below through the same gap between the two bars inside the buckle in both cases. The bar on the right (the adjustable side) is very close to the tabbed side of the buckle. And there are teeth on the topside of the buckle bar on that side to keep the webbing from slipping. To release the tension on the strap the tab side of the buckle is lifted which lets the webbing run out.