Learn Spanish (Latin America): Hay suficientes sillas para los invitados.

In this lesson you're learning about adverbs, which don't change form. However, in this specific sentence, suficientes is acting as an adjective because it describes a noun (sillas). Since sillas is plural, suficientes must be plural too. If it were describing an action instead (like "I slept enough"), it would be an adverb and stay singular as suficiente.

Why does suficientes come before sillas? I thought adjectives usually go after the noun in Spanish.

Descriptive adjectives (like colors or sizes) usually go after the noun. However, adjectives of quantity—words that tell you "how much" or "how many," like suficiente, mucho, or numbers—almost always go before the noun they describe.

Could I use están instead of hay since "chairs" is plural?

No, because you are simply stating that the chairs exist ("there are"). To say "there is" or "there are" in Spanish, you always use hay, which never changes to a plural form. You would only use están if you were talking about where specific chairs are located (like "Las sillas están en la cocina").

Why do we use para instead of por in this sentence?