Learn French: Les femmes sont ici, elles sont fortes. - The women are here, they are strong.

Because "they" refers back to les femmes (the women). In French, you use the pronoun elles for a group of females or feminine nouns. If the group was male or a mix of males and females, you would use ils.

Why is the verb sont used for both parts of the sentence?

Sont is the "they" form of the verb être (to be). It is used anytime the subject is a plural third party. It matches both the plural noun les femmes (the women are) and the plural pronoun elles (they are).

Why does the adjective fortes end with both an "e" and an "s"?

Adjectives must match the word they describe. The base word for strong is fort. Since it describes les femmes, we add an "e" because it is feminine, and an "s" because it is plural.

Do you pronounce the "s" at the end of femmes, elles, or fortes?

No, those final "s" endings are completely silent! In spoken French, you can tell the sentence is plural because you hear les instead of la, and sont instead of est.