The Garda hitch is a very useful tool for crevasse rescue, ascending a rope, or hauling a pack or small haul bag. It works by pinching the climbing rope between two carabiners. It is important with the Garda that the loads be static in nature (do not use it for belaying), and that the carabiners used are identical in size (non-lockers are best).
Here is a short, non-exhaustive, primer on the Garda that I filmed during a recent Alpine Mountaineering course on the Kahiltna Glacier of the Alaska Range. As with all new skills, tying and using the Garda Hitch requires practice and proper application.