GPUs are specialized computers used to accelerate "Matrix Multiplication". Traditionally, matrix-multiplication was used to calculate 3d objects vs the camera / screen... a very common operation in video games. There's a bit of math and study involved in this, but this picture should give you the idea:

GPUs are designed to perform this operation trillions-of-times per second, because video games have a lot of objects on the screen that move around (rotate / animate, etc. etc.), that needs to be simulated in this manner. So any video game will have a powerful, dedicated computer specifically designed for this matrix-multiplication operation.

About... 15ish years ago, someone created the "Tensor" operation for Deep Learning Neural Networks. This allowed ANNs to be written as a matrix-multiplication problem, and therefore accelerated on a GPU. GPUs after all, are the fastest computers we got for Matrix Multiplication.