As Nick suggested you flick the filters in front of your eye to see the colour changes. I find these filters very useful , I will make a correction in my mind without using these filters and then use them to verify my thoughts on the colour.
Laying them closer to the print the effect is stronger, halfway to your eye and print is the normal proceedure, and right on your eye the effect is less strong.
Micheal, doing a colour ring around is a critical step in learning about colour and how the enlarger dials affect the balance.
To do a colour ring around will take the better part of an afternoon but once done properly you will have a reference that is invaluable for all your future colour corrections.