GPU (graphics processing unit) takes data and shaders which are usually preprocessed by the CPU (central processing unit), processes them according to its own rules, and then sends them back.
Many people think of a computer as a machine for crunching numbers. Computers process information in 1s-and-0s. CPUs do this math quickly because they use logic chips designed specifically for mathematical operations. But a CPU can only process one calculation at a time, so there need to be lots of these chips working together in parallel if we want things to get done fast.