WTF usually refers to 'what the fuck'. It can be used as a question, an exclamation, and many other uses.
It is commonly used in internet chatrooms where swearing is censored.
The 'W' can be used as what, where, who or when, following by the 'TF' which is always 'the fuck'
WTF is usually used with dude or mate
Example 1: WTF just happened here?
Example 2: Dude, WTF!
Example 3: WTF did that?
Example 3 uses 'who' instead of 'what'