A GPU processes all the stuff that you end up seeing on your screen.

A CPU processes all the stuff that you need in order to see things on the screen.

Most CPUs have “integrated” GPUs...so an “Intel i5” CPU could have an integrated “Intel HD 5000” GPU.

An NVidia GPU is usually “discreet” or separate from the CPU. In a desktop this takes the form of a “graphics card” that you would plug into a special expansion slot on the motherboard. These will normally have an order of magnitude better graphics processing power than an integrated GPU. That means you can have smoother and more detailed 3D graphics on your screen.

NVidia is a manufacturer of GPUs. Another manufacturer of GPUs would be AMD.