Learn French: Le cavalier met la selle, et le cheval reste docile. - The rider puts on the saddle, and the horse remains docile.

To add an exclamatory emphasis, you could say Reste-t-il docile, ce cheval ! or Est-il docile, ce cheval ! By using the inverted question structure (verb + subject pronoun) before an adjective, you create a stylistic exclamation. Since le cheval is a noun, you state the noun first and then use complex inversion with the pronoun il.

Is a cavalier the same thing as a knight?

Not exactly, though they share the same root. A cavalier (or cavalière) is simply a horseback rider or equestrian. If you want to talk about a medieval knight in armor, the French word is chevalier.

Why do we use met (from mettre) for putting a saddle on a horse?

The verb mettre is extremely versatile. Just as you use it for putting on your own clothes (for example, mettre un manteau), you use it for putting gear or equipment onto an animal. You do not need to add a preposition like sur; mettre la selle naturally translates to putting the saddle on.

French usually avoids commas before et (and). Why is there one here?