Learn French: Parce qu'il y a un embouteillage dans le centre-ville. - Because there is a traffic jam in the city center.

Parce que means "because". When the word right after it starts with a vowel, like the i in il, the e at the end of que is dropped and replaced with an apostrophe. This is called elision, and it makes the phrase flow much more smoothly when you speak!

I thought il meant "he". Why does this sentence translate it to "there is"?

You are exactly right that il usually means "he" or "it". However, il y a is a very common fixed expression in French that translates as "there is" or "there are". In this specific grouping of words, il doesn't refer to a specific person.

Why use dans le for "in the" city center? Could I use au?

Dans means "in" or "inside" and is followed by an article like le (the). Using dans le centre-ville emphasizes being physically inside the downtown area where the traffic jam is happening. You will also frequently hear au centre-ville (at the city center), which is completely fine to use too!

Why is it formed as centre-ville instead of ville-centre?