Rather than make up an answer, I googled and am posting from the first blog I found:
- Proper names in Modern Greek always take a definite article. It’s quite rare in English: rivers, families, plural countries.
- Nouns with generic reference take a definite article in Modern Greek and not in English: Gentlemen prefer blondes in Greek is Οι άντρες προτιμούν τις ξανθιές.
As for the indefinite article, it’s mandatory in English where it applies; it’s often optional in Greek. So I saw a car = είδα (ένα) αυτοκίνητο.