A typical online guide for using the tool describes it this way: "Copy the sequence of numbers in cell Result through Step 2. Visit the page https://www.mrchecker.net/card/ccn2 Paste the number sequence Result enter, and press Start. Wait a moment to see which card can be used, see in the green Live box".
The online landscape is filled with similar services. Some notable competitors and alternatives to MrChecker in this space include: mrchecker ccn2 top