一面墙，和一支能写在墙上的笔。A wall, and something to write on it.
谁都可以留一张便签：挑一张纸，署不署名随意，一百二十个字以内。没有人读过之前，它不会出现在墙上。
Anyone can leave a note. Paper, a name if you want one, and a hundred and twenty characters. Nothing appears on the wall until it has been read.
墙上还是空的。下面那张便签，可以是第一张。
The wall is empty. The note you write below can be the first one.