When should I use the present subjunctive and the present indicative?

The present indicative means what you (or whoever the verb is talking about) is doing right now. There is no doubt about it, you are simply indicating it. For example; "I drive," "you make" "we go" are all definite, with no doubt or possibility. It is the most commonly used tense when referring to the here and now.

However, the present subjunctive is used when there is some doubt about the action being described. For example, to use a common structure that we have in English, "If I were rich, I would go to Spain." The subjunctive may also be "triggered" after certain phrases, normally certain opinion phrases, phrases referring to wanting someone to do something and phrases of doubt. For example, "Dudo que haya tiempo para eso," (I doubt there's time for that) or "Es importante que aprendamos un idioma diferente." (It is important to learn a different language). By far the most common use is that of wanting someone to do something, what is known as verbs of influence or willing, such as "Quiero que vengas conmigo hoy." (I want you to come with me today).