Spanish is the official language of Guatemala, and the most commonly spoken. Over twenty indigenous languages are still spoken throughout, but many of the Maya people have at least a working knowledge of basic Spanish as well, except in the more remote areas. For the Garifuna people in Livingston, Garifuna and English are the main languages (but Spanish is spoken as well).
The most familiar form of Spanish spoken among good friends is the "tú" and "vos" form, but varies between regions. It is considered rude and very informal if used with someone that you do not know. As a tourist, it is safer to stick with the "usted" form. However, don't be surprised if some homestay families and some language teachers jump right into using the "tú" or "vos" form. If they do, you may respond in kind.