Cars are complicated
Vehicles are a complicated and necessary part of everyday modern life. Most people choose to just drive their car without digging in to how it works. That's okay! We're guessing that's you, if you're asking this question. A quick understanding of your car will help you understand the difference between an auto body shop and an auto repair shop.
To drastically simplify, your vehicle has two basic divisions: The engine, which provides the power to move, and the body, which holds the engine, passengers, and everything else.
A normal auto repair shop will fix engine components and related parts that wear out during normal driving, whereas a body shop fixes the body: frame, doors, windows, bumpers, etc. These parts aren't involved mechanically in powering the vehicle or bringing it to a stop.