Your Graphics Processing Unit (GPU), or Graphics Card is a specialized processor dedicated to enhancing visual display functions on your PC. Generally speaking, it's used for processes common in modern games, such as:
However, GPUs have a wide variety of uses outside of running and developing games. In case you're interested, here's how Salad uses your GPU to make you money. Unfortunately, this requires your GPU to have 4+ GB VRAM, which means you'll need a relatively high-powered card to chop some Salad. So how do you find that out?
First, go to your windows home button and search for "Device Manager" - here's a link on how to find it, in case it's being sneaky. Once in device manager, open the "Display Adapters" tab and click on it.
Of course, it may look a bit different if you're on a different OS of Windows. Once you find the model number of your GPU you can look it up online. Typically the manufacturer has a page listing the technical specs of their specific hardware, and on this page you'll find your card's VRAM.
If you have multiple GPUs like above, check out this FAQ here.