A Raspberry Pi is a single-board computer (SBC) which can be used for projects both on and off the robot, including:
Vision systems (including Machine Learning with additional hardware)
Simplified control systems for outreach (non-competition) robots
A general learning environment for skills like programming, linux, computer vision, and more.
While there are other SBCs out there (Arduino, Orange Pi, etc.), the rPi boards are cost effective, moderately powered, and have an extremely broad ecosystem of peripherals and tools developed by an enthusiastic community.
After following the links below, you will have your rPi powered on, imaged, and connected to a laptop with a development environment.