There are two kinds of burial chamber that are refered to as cists or kists. Kist is usually used to refer to a megalithic structure and cist used for later Bronze Age burials.
Cists are small slab lined boxes, set into the ground, with a single slab used as a cover. They tend to be no larger than 1.5m square. Although cists are found in dedicated mounds or cairns they are often later insertions into megalithic cairns (see Kilmashogue (County Dublin)).
Kists are much bigger structures and usually built above ground level (see Dolmen of the Four Maols (County Mayo))and covered by a cairn. They are usually rectangular in plan with vertical sides, but one type, known as a Linkardstown Kist is pentagonal with sloping side stones (see Cloghtogle (County Fermanagh)).
A kerb is a ring of stones placed around the perimeter of a burial mound or cairn. It basically serves the purpose of a retaining wall to keep the cairn or earth in place. Kerbs are usually associated with passage tombs, but do occur on court tombs and wedge tombs too.
Sometimes on passage tombs the stones can bear decoration, such as at Newgrange (County Meath).