QUE as a conjunction
We have seen above that que can be used as a relative pronoun in which case it refers to a word or group of words previously mentioned (or which are identifiable through the context)
However, it is also very important to be aware of the fact that que can often be used as a conjunction introducing a subordinate clause. For example: Il dit que le président s'est trompé, which in English can be translated as He says (that) the president was mistaken. Note that in English, the conjunction can sometimes be left out, but that this is not the case in French.
The conjunction que can also be part of an expression of comparison: La situation est plus grave qu'ils le pensent mais pas aussi désespérée que tu le dis. (The situation is more serious than they think but not as desperate as you say)
As is the case with the relative pronoun, que, when used as a conjunction, will also become qu' in front of a vowel or an h.