Learn Portuguese (Portugal): Nós estamos em frente do cinema.

The word do is a combination of de (of) and o (the). Because cinema is a masculine noun, it needs the masculine word for "the" (o) before it. In Portuguese, de + o always merges into do.

Can I just say em frente o cinema and skip the de completely?

No, you always need de (or its combined forms like do or da) to connect these location phrases to a noun. Just like in English where we say "in front of the cinema", Portuguese requires that "of" connection.

Why do we use estamos for "we are" instead of somos?

Portuguese has two verbs for "to be": estar and ser. You use estar (and its "we" form, estamos) to talk about physical locations. Ser (somos) is used for permanent characteristics, like your nationality.

Do I have to include the word Nós at the beginning?