Learn French: Elles boivent une tasse de thé sur la terrasse. - They drink a cup of tea on the terrace.

No, the -ent ending on French verbs used with ils or elles is always silent. You just pronounce the first part, which sounds a bit like "bwav".

Why does boivent have a "v" in it?

The verb boire (to drink) is irregular. For singular subjects like je or elle, it uses the stem boi- (as in elle boit). But for plural subjects like nous, vous, and ils/elles, the spelling changes and introduces a "v". For elles, it becomes boivent.

Why is it une tasse de thé and not une tasse du thé?

When you use a noun that measures a specific quantity, like une tasse (a cup) or un verre (a glass), it is always followed by just de or d'. You drop the le, la, or les that would normally combine with it to make du or des.

When should I use elles instead of ils for "they"?

You use elles when the group of people or things you are talking about is entirely feminine. If the group is all masculine, or a mix of masculine and feminine, you must use ils.