Learn Portuguese (Portugal): O rapaz está em frente da árvore.

The base phrase for "in front of" taught in this lesson is em frente de. Because árvore (tree) is a feminine noun, it requires the feminine word for "the", which is a. In Portuguese, de and a must blend together to form the contraction da.

Why do we use está here instead of é for the word "is"?

We use está (from the verb estar) because it describes a physical location. Whether the position is temporary (a boy standing) or permanent (a building), you always use estar to talk about where someone or something is located.

How can I tell if a word like árvore is masculine or feminine?

Árvore is feminine. Nouns that end in -e can be either masculine or feminine in Portuguese, so you generally just have to memorize their gender. However, you can spot that it's feminine right here in the sentence because of the da (de + a) right before it!

Does the word frente just mean "front"?