Learn French: Mon oncle et ma tante regardent un film. - My uncle and my aunt are watching a movie.

In French, possessive words like "my" must match the gender of the noun they belong to, not the person speaking. Since oncle (uncle) is a masculine word, you use mon. Because tante (aunt) is a feminine word, you use ma.

Can I just say mon oncle et tante like "my uncle and aunt" in English?

No, in French you generally cannot skip these small words before a noun in a list. You have to repeat the "my" for each person: mon oncle et ma tante (literally "my uncle and my aunt").

Why does the verb regardent end in -ent?

The subject doing the action is mon oncle et ma tante (my uncle and my aunt). Together, they count as "they" (ils). For regular -er verbs like regarder (to watch), the "they" form always ends in -ent. Remember that this -ent ending is completely silent!

The translation says "are watching", so why is there no word for "are" in the French sentence?

French doesn't have a separate "are doing" or "is doing" tense. The single present tense verb regardent translates to both "watch" and "are watching" depending on what makes sense in English.