In English, the subjunctive mood appears in expressions of counterfactual ideas (If I were smart), desires (I wish he were kinder), proposals (I suggest she take over), commands or demands (I insist they be present), and suppositions (I would be glad if he were to sit here). Unlike indicative phrasing (which, compared to the above examples, would require simple present verbs), subjunctive phrasing creates a feeling of the uncertainty of will.
To construct a subjunctive clause in the present tense, verbs take the base (infinitive) form: I suggest that he write, I demand you be present, She must wash her hands (compare to their indicative forms: he writes, you are, she washes). In the past tense, verbs take the simple past form, except be, which becomes were: I wish I were smarter, If only he took the bus. In the pluperfect tense, verbs take the past-perfect mood: If he had taken the bus.
Subjunctive mood also lends itself to a few popular idiomatic phrases, especially those involving god: God bless, God forbid, God save the Queen, Lord help us, be that as it may, would that it were, and suffice it to say.