A mood shows the attitude (point of view) of the speaker or writer toward what he is saying or writing.
There are following moods of verbs: indicative, imperative, interrogative, conditional and subjunctive.
We use it to express facts and statements:
It occurs in commands and instructions:
Negative commands are formed with don't + base verb form:
We need this mood to form questions:
It’s used to make requests and to talk about uncertain situations:
It's not so important in English in opposite to other languages like French or Italian.
Using the subjunctive we express a wish, emotion, doubt, desire or possibility.
a) It occurs in formal writing with that and with verbs such as suggest, demand, insist, ask, recommend, etc.:
b) The other use is of the subjunctive is after if, as if/as though, in sentences that express wishes and hopes that cannot be fulfilled:
c) Subjunctive is used in some well known fixed phrases: