Well if it's facebook......on a computer all 你 have to do is type your status and if 你 wanna say their name in a status....for example "I 爱情 my sister, Carrie" Just start typing they're name and it will 显示 up.....but only on the computer/laptop.
If 你 mean on Facebook, underneath where 你 have written your status there is a grey picture of a person with a plus sign 下一个 to it- click on that and choose who 你 wish to tag, 或者 just type their 脸谱 name in your status.