Answer:
Le (masc. singular), La (fem. singular), L' (followed by a vowel), and Les (plural)
Examples of these 4:
le garçon – the boy
l’homme – the man
la femme – the woman
l’amie – the friend (girl)
les enfants – the children
When are they used:
Le and la are used before masculine and feminine nouns (with no liaison).
If the noun has a liaison, use l' for both masculine and feminine nouns of this type.
Les is the plural version of le and la.