Here's another one that sort of explains how AI and computers work (sort of):
Imagine you’re in a room with the door closed, surrounded by books. You’re given instructions to follow. Someone outside slips a piece of paper under the door; it has a message written in Japanese, which you can’t read or understand. Your instructions say that whenever you see a certain Japanese symbol or group of symbols, you should look through the books until you find a match. The book will tell you, in parentheses, what symbols to write in response for each group you find. You copy those symbols onto a new slip of paper and slide it back under the door. To the person outside, it seems like you understand Japanese.
I am sorry, but I couldn't understand the entire first half of that sentence.
They are referring to how your first message could be easily perceived as discussing politics and sensitive issues, which are presumably not allowed on this forum. Therefor, they're saying they're 'in' the thread 'b4' (before) 'the' thread is forcibly 'lock'ed by site admins.