The subjunctive is used mostly with verbs or adverbs expressing desire, doubt, order, or occurrence. Almost always preceded by que (that).

Similar uses to English:

Demand, command, encourage to do something Il faut qu’elle comprenne cela ("t is necessary that she understand that)

Expressing a desire to do the act denoted by the root verb eg Vive le roi!

Subordinate clauses: for example with although and before, the subjunctive is used

Bien que ce soit ton anniversaire (Although/even though it is your birthday)

Avant que je m’en aille (Before I go away)

Imperfect subjunctive - used in older, formal, or literary writing, replaces the present subjunctive in a subordinate clause when the main clause is in a past tense.