Learn Portuguese (Portugal): Nós temos dezasseis chaves no escritório.

Temos is the "we" form of the irregular verb ter (to have). Because the subject is nós (we), we use temos. Note that in Portuguese, you can often drop the pronoun and just say Temos dezasseis chaves... since the verb itself already tells us it means "we have".

Is dezasseis spelled differently in European Portuguese?

Yes! In Portugal, 16 is spelled and pronounced dezasseis (with an a). If you happen to see dezesseis (with an e), that is the Brazilian Portuguese spelling.

How do we form the plural for chaves?

To make a noun plural in Portuguese, you usually just add an s if the singular word ends in a vowel. Since the singular word for key is chave, adding an s gives us chaves.

Why does the sentence use no for "in the" instead of just em?

The word no is a mandatory combination (contraction) of the word em (in) and the masculine word for "the", which is o. Because "office" is a masculine word (o escritório), em + o merges into no.