Different gamepads and other controllers can appeal to different types of gamers, depending on your budget, taste, and platform of choice. You can’t play video games without a good control system. Maybe you want a keyboard and mouse for your shooters and strategy titles. Maybe you don’t mind using a touch screen for smartphone puzzles. Most games, though, play best with some form of dedicated controller. That’s why every major game console comes with a gamepad or two, and why they all can be connected to your PC with some tinkering.
If you mostly want to play games on your PC, for the very good reason that it has the largest library of titles spanning the widest range of ages, audiences, genres, prices, and hardware requirements, you should probably invest in some form of controller. There’s nothing wrong with playing Fortnite or Overwatch with your current mouse and keyboard, but almost every other game you pick up from Blizzard, GOG.com, Humble Bundle, or Steam will feel much better with dual analog sticks under your thumbs.