Keywords: what, that, which
1. Used alone to ask people what they are talking about, especially if you suspect it has something to do with you. English = 'What?', 'What was that?' and so on.
1. Often used immediately after a noun and before a descriptive phrase or clause which gives further information about the first noun. English = that, which. Non-standard English = what.
1. Used at the beginning, end, or at both the beginning and the end of sentences when you are asking for information about something. English = what.