How are unmatching and blocking different?
Unmatching and blocking are the same thing.
Blocking or unmatching someone will prevent them from seeing your profile -- if they try to view your profile after you block/unmatch them, it will look just like you deleted your OkCupid account.
If you've had a conversation with them, blocking/unmatching will also remove the conversation from their Conversations page. We do not otherwise let people know that you have blocked or unmatched them.
On the website you can block people from their profiles by clicking the three dots icon at the top of the page, or within the conversation window. You can view your list of blocked/unmatched members on the privacy settings page.
On the app, you can block people by tapping the three dots icon at the top of their profile, or by tapping on the icon on the top right when viewing a received message to see a block button pop up. You can view your blocked/unmatched users on the app by going to settings (look for the gear icon at the top of your profile), then tapping on Privacy, then on Blocked & Unmatched.
Note: Passing someone does not block them. Passing just means you won't see them around the site until you run out of people to see. If you do run out of people to see, we'll recycle your passes so you have another chance to see them- after all, many people will upload another photo or write more about themselves since the last time you saw them, and will be much more interesting!
You can read about other privacy controls here.