This is an attachment for tripod heads designed to make it quicker to remove the camera for handheld photography and re-attach it. You attach the quick release plate to the camera with a slotted screw or butterfly nut, then clip the quick release plate on to the tripod head with a sprung catch or a locking screw. Quick release plates come in different types, but the closest to a universal standard is the Arca Swiss plate.
Many tripod heads come with quick release camera plates, and while some are specific to that tripod maker and tripod, which can be annoying, Arca Swiss plates use a standard design that means they should be interchangeable across tripod brands. It’s a good selling point in a tripod head.
Tripods usually come with rubber feet on their legs, but these may not give much grip or purchase if you’re using them outdoors on soft or uneven surfaces – this is where it’s often better to have a metal spike instead. On some tripods, the rubber feet will screw back to expose a spike. On others, you may be able to unscrew the rubber feet and screw on spikes instead.
Cheaper tripods use aluminium legs which keeps costs down but does add to the weight. This isn’t usually a problem if you’re travelling short distances or working from the back of your car, but if you’re taking a travel tripod on a vacation or hiking any great distance, a more expensive carbon fibre tripod will give a better balance between rigidity and weight.