ECU Code?

I just have a quick question.. I want to check my ECU for errors.. How do I do this.. I keep hearing about checking the light codes.. but I dont have any idea what they are talking about.. can someone help me?

Pull back the carpet on your passengers side, you should see a copperish colored plate - in the center of it should be a hole with a plastic cover behind it. IF your check engine light is on (when the car is running) then there should be a red blinking light behind that clear plastic window. Just count the number of times it blinks then refer to the code list to see what's wrong.

thanks