It looks like a hammer and it works like a hammer because you pound with it. There are many kinds of mallet, some are used in carpentry, others for machinery and there’s the kind used for cooking.
One side of the head of a kitchen mallet is spiked to tenderize meat. The opposite side is smooth which is good for flattening meat. Both sides are used with the same pounding motion.
Why flatten meat? To make a piece of meat of uniform thickness so that it gets cooked evenly.
When buying a kitchen mallet, make sure that the wood is of good quality and that the head is securely attached to the handle. The mallet that you see in the photos is my second, the first one (cheap) didn’t last very long as the head kept getting loose while pounding meat.
To use the kitchen mallet, it is best to place the meat between two sheets of cling wrap (or wax paper although wax paper will get poked with holes if using the spiked side of the mallet). Start pounding at the center working your way outward. Check the meat after pounding a few times and make sure that you have not overdone the pounding and caused the meat to tear before you resume the pounding.