The nice thing about the verb ir is that it does double duty: not only can you use it to describe where you’re going, you can also use it to talk about what you’re going to do. To do this, we need to add the preposition a and an infinitive.

• Ella va a comprar el libro. (She is going to buy a book.)

This might seem confusing, since we just learned that ir + a describes where you’re going. The trick is to look for the infinitive verb. If it’s there, we’re talking about what we’re going to do, if it’s not, we’re talking about where we’re going.

• ir + a + infinitive:
  Yo voy a estudiar esta noche. (I am going to study tonight.)
• ir + a (no infinitive):
  Yo voy al cine esta noche. (I am going to the cinema tonight.)