Power racks and squat racks work by giving a loaded barbell a stable place to start, rest, and be caught when a lift gets difficult. The rack does not lift the weight for the user. It provides structure around barbell movements so squats, presses, rack pulls, and related lifts can be set up more predictably.
A power rack usually surrounds the lifter with uprights and safeties. A squat rack is often simpler and more open. The important parts are the uprights, hooks, safeties, pull-up bar, hole spacing, weight capacity, and enough room to move the bar safely.