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.

Italian also has a past subjunctive that describes past events in the same way as above.