Learn French: Je prends un sandwich et un jus, parce que j'ai faim. - I am having a sandwich and a juice, because I am hungry.

Yes, prendre generally means 'to take'. However, in French, you use prendre when talking about consuming food or drinks. While in English you say 'I am having a sandwich', a French speaker says Je prends un sandwich (which literally means 'I take a sandwich').

Why does the sentence use j'ai faim instead of the verb to be (je suis) for 'I am hungry'?

In French, hunger is something you have, not something you are. Faim is a noun meaning 'hunger', so you use the verb avoir (to have). Therefore, j'ai faim translates literally to 'I have hunger'.

Why does prends end with an 's' here? Don't 'I' forms usually end in 'e'?

Regular French verbs ending in '-er' do take an 'e' with je, but prendre is an irregular verb that ends in '-re'. For many '-re' verbs, the je (I) and tu (you) forms end in an 's'.

Why is 'because' translated as two words (parce que)?

That is just how the word is built in French. You should treat parce que as a single fixed expression meaning 'because' and learn it as one vocabulary item.

Why is it written as j'ai and not je ai?