1. To declare intentions or make predictions:
• Iremos a Irlanda en enero*.
  • We will go to Ireland in January.
• En el año 2100, habrá colonias en la luna.
  • In the year 2100, there will be colonies on the moon.
2. To forcefully express an order:
• ¡Volverás a casa y limpiarás tu cuarto!
  • You will go back home and you will clean your room!
3. To express conjecture or probability concerning a present-tense event:
   • No sé cuál es el cumpleaños de Mariana. Lo sabrá su madre.
     • I don't know what Mariana's birthday is. Her mother probably knows.
   • ¿Cuántos años tendrá esa señora?
     • How old do you suppose that lady is?

*As in English, declarations of future intent like this one can be expressed using the present:

• Vamos / vamos a ir (we're going / going to go) a Irlanda en enero.

However, unlike English, Spanish does not use the present progressive* to express the future:

• We're leaving* at 9:00. Salimos / Saldremos / Vamos a salir a las 9:00.