How do i use this wheel with an encoder please ?

Using Arduino Project Guidance
1

Hi, Ive got a small platform driven by two wheels, the third wheel just swivels in any direction. I am using the L298N Motor driver which is very easy to wireup. But I want to count the revolutions of the wheels. The motors and wheels came with a couple of the little disks you can see in the photo. I dont know how they are supposed to help me ? What is an encoder or how do I implement one to track the wheel revolutions ?

Is there a good youtube video to show me how, I havent found one.

Thanks, Mike.

2

Those little disks you mention are supposed to be used with a speed encoder like this one :40 Pin ZIF DIP IC Tester Board Socket - Green - Free shipping - DealExtreme