The Spanish "subjunctive" is used to express emotions and feelings as opposed to "indicative" which refers to actual (or likely) events.

Brief overview of uses:

Present Subjunctive (view lesson here)
- Emotions today and tomorrow about something being done today or tomorrow.

Imperfect Subjunctive (view lesson here)
- Emotions yesterday about something done before yesterday and conditional sentences referring to something unreal today or tomorrow.

Present Perfect Subjunctive (view lesson here)
- Emotions today and tomorrow about something done yesterday.

Past Perfect Subjunctive (view lesson here)
- Conditional sentences referring to something unreal yesterday.