Learn French: Elle est française.

Because it describes Elle (she), which is feminine. In French, adjectives must match the gender of the person or thing they describe. To make the masculine adjective français feminine, we simply add an -e to the end to get française.

Does adding the -e change the pronunciation?

Yes! In the masculine form français, the final -s is silent. However, adding the -e to make it française forces you to pronounce that -s, which ends up sounding like an English "z".

Why isn't française capitalized like "French" is in English?

In French, nationalities are only capitalized when they are used as nouns to refer to a person (like une Française for "a French woman"). When used as an adjective to describe someone, as it is in this sentence, it is always written with a lowercase letter.

I sometimes confuse est with et. What is the difference?

est means "is" and comes from the verb être (to be). et simply means "and". While they look similar, remember that est is a verb that connects a person to their description, which is exactly what is happening here.