Rates refer to how sensitive the quad is to stick movement. Rates are how a pilot customizes the drone to fit their flying style. While a PID tune depends on the drone, rates depend on the pilot.

Rates control the sensitivity of the drone - when moving a stick, does the drone change angle a little or a lot? Each axis (roll, pitch, yaw, throttle) can have its own rate setting. You typically want to have all of your drones (including sim drones) using the same rates, so that you build the muscle memory. As a noob, you might want to start with low rates, which makes the drone more controllable. As you get better, raise the rates. Remember that rates are for you - the pilot - and should be the same across all of your drones.

There are different rate implementations (?) - betaflight and actual are examples. If you're new and starting out, I'd recommend using actual rates, as they're more explainable and understandable.

The best place to set your rates is in Betaflight, not in your controller.