When you come across someone on CatholicMatch, you may or may not need to do anything at all. Here is a breakdown of different areas of the site where you may encounter other members and what to do when you simply aren't interested:
When you come across someone in your search results who doesn't interest you, you may snooze the profile if you'd like. This way, you won't continue to see that same person in your search results.
While reviewing your matches, you will be asked if you are interested in the match. If you aren't interested, click the "X" and the member will be removed from your match list.
If someone views your profile and you don't find them to be appealing, there is no need to take any action at all. They will automatically be removed from your views list 60 days after the view occurred.
If you receive a message from someone who doesn't interest you, it is completely up to your discretion how to proceed. Most members would prefer to receive a polite response of "Thank you for your message, however, I don't feel that we would be a good match." This way, they'll know to move on and find someone else of interest. If the member continues to contact you after you've let them know that you aren't interested, you can place a block.
You can also avoid receiving messages from those who don't meet your preferences, by ensuring that you've clearly outlined your requirements in your Ideal Match description, especially age and distance. That way, when someone outside of your preferences views your profile, they can simply move on to the next profile and they won't waste their time or your time sending a message since they already know that they don't meet your preferences.