When you block someone on Snapchat, they can no longer send you Snaps or messages, view your Stories, or find your profile in the search. They are automatically removed from your Friends list, and your profile becomes invisible to them. Any messages they try to send appear as "Pending" on their side but won't reach you. The blocked user still retains access to previous saved messages on their end, but no new interactions are allowed. They aren't notified directly that they've been blocked, but they may realize it by the disappearance of your profile and inability to contact you. Blocking is different from removing a friend, which only deletes them from your Friends list but does not restrict their ability to view some content or send messages. If you later unblock the person, you must send a new friend request to reconnect, and messages sent during the block won't be received.