Two Chips, Two Jobs
Almost every modern computer or phone has both a CPU and a GPU. The names are similar, both end in PU, and both are usually described as the brain of the device, which is where the confusion starts. In reality the two chips have different shapes inside, different strengths, and different jobs. They work together, but they are not interchangeable.
The CPU: A General-Purpose Brain
CPU stands for central processing unit. It is the main processor at the heart of the computer, the part that handles the wide variety of tasks an operating system and its programs throw at it. Reading a file, opening a web page, running a game's logic, deciding what to draw next — all of these go through the CPU. A CPU has a small number of powerful cores, and it is built to be very fast at running one task after another in sequence. When a piece of work cannot easily be split into many identical jobs, the CPU is the right tool.
The GPU: Built for Doing Many Small Things at Once
GPU stands for graphics processing unit. It was originally designed to draw pictures on a screen. Drawing an image means doing the same kind of calculation for every pixel: figuring out its color, its lighting, its position in 3D space. There are millions of pixels, and the calculation for each one is almost the same. The GPU is built for exactly that kind of work. It has a much larger number of smaller cores, all crunching similar calculations in parallel, side by side. That parallel design is what makes it so good at graphics, video, and certain scientific or AI workloads.
Why Modern Computers Use Both
Most everyday tasks need the flexibility of a CPU: deciding what to do, talking to files, juggling apps. As soon as you ask the machine to render a complex 3D scene, encode a video, or run a neural network full of identical math operations, you want a GPU. So computers split the work. The CPU directs the overall flow of the program and hands off the big parallel jobs to the GPU, which chews through them in a fraction of the time the CPU would take alone.
A Helpful Picture
A simple analogy helps. A CPU is like a small group of highly skilled workers who can each do almost any job, very quickly, one after another. A GPU is like a huge team of less flexible workers, all doing the same simple step on different items at the same time. Neither is "better" — they are tuned for different shapes of problem, and a modern device uses each one for what it does best.
Source
This article was written using information from Wikipedia.