Learn Dutch: Mijn auto start niet omdat hij oud is. - My car won't start because it is old.

The word omdat (because) is a subordinating conjunction. In Dutch, these types of connecting words introduce a sub-clause and push the conjugated verb (in this case, is) to the very end of that clause.

Why does it say omdat hij oud is (because he is old) instead of using a word for 'it'?

In Dutch, you use hij (he) to refer back to singular de-words, even if they are objects like a car (de auto). You only use het (it) to refer back to het-words.

The translation says the car 'won't start', but where is the Dutch word for 'won't'?

The Dutch sentence literally says 'My car starts not' (start niet). While English often uses 'will not' or 'won't' to express that a machine is refusing to work, Dutch simply uses the standard present tense to state the fact.

In the first part of the sentence (Mijn auto start niet), why does niet come after the verb?

In a regular main clause, the conjugated verb must be in the second position. Here, the subject Mijn auto is in position 1, and the verb start is in position 2. The negative word niet naturally follows the verb.