Hill Giants are the most basic of all the giant breeds iconic to the worlds of Dungeons & Dragons. Considered the smallest, weakest, and usually the stupidest of their kind, Hill Giants are basically oversized ogres; big dumb brutes who lope across the countryside, smashing things for fun and eating whatever they can get their grimy hands on.
...That's pretty much it. They're usually regarded as the least interesting of all the six "core" giant species, due to their "primitive brute" archetype. Most lore about them, regardless of edition or setting, boils down to them being basically oversized pulp-style cavemen; they typically live in caves or bear dens, though they can sometimes build primitive earthen, mud, or log huts, and spend their time looking for food or raiding the settlements of smaller, civilized races (activities that are pretty much one and the same to them). Their social lives are full of thuggish violence; they eat, sleep, brawl and rut, and that's pretty much all they do. Some sourcebooks can actually stretch this information out into reams upon reams of words - see the Pathfinder [lore], but basically this is what it all boils down to.