A computer doesn’t need a GPU.

What a GPU is good at is performing the same task on a bunch of pieces of data at the same time. You want to add 3.4 to a million numbers? The GPU will do it much faster than a CPU can. On the other hand, it can’t do a series of complex things as well as a CPU, or move stuff in and out of the computer’s memory or from storage. You can use the GPU’s special abilities for all sorts of things, but calculations involving 3D objects and geometry is a big one — it’s super useful in computer graphics (why it’s called a Graphics Processing Unit) and games. If you want stunning graphics for games, the GPU is going to be the best at doing that for you.

The CPU talks to a GPU using a piece of software called a “driver”. It uses that to hand data to the GPU, like 3D shapes and textures, and then it sends commands like “turn the view 5 degrees”, “move object 1 left 10 units”, and stuff like that. The GPU performs the necessary calculations and makes the picture available to send to the screen.

It’s also possible to program the GPU to solve math problems that involve doing the same thing to a lot of pieces of data at the same time.