Learn Portuguese (Portugal): Eles fazem poucas perguntas.

The word for "few" or "little" (pouco) changes its ending to match the noun it describes. Because perguntas (questions) is a feminine plural noun, the quantifier must also be feminine and plural: poucas.

I thought fazem means "they make" or "they do". Why is it translated as "they ask"?

In English you "ask a question", but in Portuguese you "make a question" (fazer uma pergunta). Since eles means "they", we use the matching verb form fazem. So literally, the sentence says "They make few questions."

Could I just use the verb for asking and say "Eles perguntam pouco" instead?

Yes, you could! Eles perguntam pouco means "They ask little". Notice that pouco stays in its default masculine singular form there, because it's describing the verb (how much they ask). But in our sentence, poucas is describing a specific noun (perguntas), so it has to change to match that noun's gender and number.

Is fazem a regular verb?

No, it comes from the verb fazer (to do / to make), which is highly irregular. Fazem is the form used for eles, elas, and vocês. Because it is used in so many everyday phrases like this one, its irregular forms are very important to memorize.