[DonRotolo]

With a general question, you get a general answer.

The encoder delivers a fixed and known number of pulses per revolution. If you have a 200 pulse-per-revolution encoder, for example, each time the shaft to which it is mounted turns one revolution, your RoboRIO will see 200 pulses.

If you then calculate how far your robot goes in one revolution - Pi is your friend here - you can then measure distance by counting pulses. This is known as Odometry.

Many encoders have a second "orthagonal" output, which can be used to determine the direction of rotation.

Also be aware that some encoders do not output pulses, but instead a variable voltage or some other 'thing' - and we're not discussing those kinds of encoders here.

Good luck!