The Italian subjunctive mood is one of the most difficult concepts for English speakers to learn. While English has a subjunctive mood, its grammatical formulations aren't quite as different from the indicative tenses.
You use the subjunctive for various reasons:
cases of desire Io desidero che vengano.
I hope that they come.
to express doubt Credo che lui vada.
I believe that he will go.
to make impersonal emotional statements È bene che sia supportato.
How good that it is supported.
to talk about impeding events Quando ti vada, mandami saluti.
When you go, say "hi" for me.