El subjuntivo en general

There are particular uses for the SUBJUNCTIVE and it's very formulaic. There are clear rules for how the sentences are structured. Compare these sentences:

• Yo quiero venir a la fiesta. I want to come to the party.
• Yo quiero que él venga a la fiesta. I want him to come to the party. (or more literally, I want that he come to the party.)

The first sentence uses the INDICATIVE. It simply makes a statement about me.

The second sentence has 2 conjugated verbs: quiero y venga. Quiero is indicative y venga is subjunctive. In this sentence, I tell what I want someone else to do.

This is a crucial point for knowing whether to use subjunctive or not. Subjunctive is used to express desires, wishes, recommendations, doubts, and emotional reactions AND there will be 2 verbs with different subjects. (Yes, there are an extremely limited number of examples using just one verb, but it's best to learn that it will use two.) This doesn't mean that every time I say I want something I now use subjunctive. Just like in the examples above, I only use subjunctive if I say I want someone else to do something (2 subjects: I and the other person). I still tell my emotions in the indicative: Estoy contenta. However, if I tell my emotional reaction to what someone else does, I will end up using subjunctive: Estoy contenta que él venga a la fiesta.

Open the following document "Subjunctive Basics" for a more detailed explanation of how to tell when you need the subjunctive.