却 (què) is used to indicate something was contrary to expectations, and is used in a similar way to 倒. However, it is generally followed by a negative comment:
The overall structure of sentences that use 却 is something like this:
Sentence， Subj. + 却 + ⋯⋯
Normally the first clause above makes a statement, and then the second clause introduces something contrary, generally in the form of a negative comment.
It's also important to point out that 却 is not a conjunction; it's an adverb. Practically speaking, this means that rather than joining two statements, it goes inside a statement (within the second clause). Specifically, it needs to come after the subject and before the verb. (Note that when you use a conjunction like 但是 it comes before the subject! 却 is different in this respect. Also, rather than replacing 但是, it can work with it to add emphasis.
Also, sometimes the subject of the second clause will be omitted. If there is a subject, however, 却 definitely needs to come after it.
In the following examples, take note that 却 comes after the subject in each case, and that it can be used together with 但是.