Let's say you want to send a message to all of your friends, even when your friends are at home eating dinner with their parents. You tell all your friends "I will leave messages in the treehouse." Then when you want to send them a message, you write it down and leave it in the treehouse. When your friends are done with dinner, they come to the treehouse to read your messages. The treehouse is your 'outbox'.

Let's say one of your friends Joe, he is in a wheelchair and can't climb up into your treehouse. So a friend of his copies down all the messages onto new pieces of paper and brings them to him. This friend of Joe's is a 'client proxy'.

Let's say Joe, since he is in that wheelchair, he tells all his friends "If you want to contact me, please leave messages in my parent's mailbox, because I can't climb into that treehouse." This is his 'inbox'. Any message that he is copied on, mentioned on, or is a DM to him, gets a copy put into his parent's mailbox so he can find it and read it.

Let's say some construction company buys the property with the treehouse and cuts down the tree and starts building a supermarket. This is 'censorship'.

Let's say you then come up with 3 different places where you put every note, each place getting an exact copy. All of these places are your 'outboxes' and the likelyhood that all of them would be taken down is low, so your messages are somewhat 'censorship resistant'.