Learn Portuguese (Portugal): Eles querem fazer o trabalho.

When you combine the verb querer (to want) with another action, only the first verb changes to match the subject (Eles querem). The second verb stays in the infinitive, or dictionary form (fazer), just like we say "want to do" in English.

Why do we use querem here and not quer?

Querem is the "they" form of the verb querer. Since the subject is Eles (they), we use the plural form. You would use quer if the subject was singular, like Ele (he) or Ela (she).

Does fazer mean "to do" or "to make"?

It means both! Portuguese uses the same verb, fazer, for "to do" and "to make". You can tell from the context which one sounds better in English. For o trabalho (the work), "to do" is the natural choice.

What is the purpose of the o before trabalho?

O is the Portuguese word for "the" when talking about a masculine, singular noun. Because trabalho ends in -o, it is masculine, so it requires the matching article o.