Learn Italian: L'uomo vende la macchina vecchia.

Vendere (to sell) is a regular -ere verb. Because the subject is l'uomo (the man, which is a third-person singular "he"), we drop the -ere ending and add -e to get vende.

Why is the order macchina vecchia instead of vecchia macchina?

In Italian, descriptive adjectives like vecchia (old) almost always come right after the noun they describe, unlike in English. So literally, the sentence says "the car old".

Why does vecchia end in -a?

Adjectives must match the gender and number of the noun they describe. Because macchina is a feminine singular noun, the standard dictionary form of the adjective (vecchio) changes its ending to -a to become vecchia.

Why does the sentence use L'uomo instead of Il uomo?

Uomo is a masculine noun that starts with a vowel. For masculine singular words starting with a vowel, the definite article (the word for "the") drops its vowel and becomes l' instead of il or lo to make it smoother to say.