Learn Spanish (Latin America): El restaurante está cerrado ahora.

We use está (from estar) because being closed is a temporary state or condition of the restaurant. We use estar for how things are right now. Ser is used for permanent identities or traits, so saying es cerrado wouldn't make sense here.

Why does cerrado end in an -o?

In Spanish, words that describe a noun (adjectives) must match its gender. Because el restaurante is a masculine noun, cerrado takes the masculine -o ending. If we were talking about a door (la puerta, feminine), we would say La puerta está cerrada.

Is there a rule for nouns that end in -e like restaurante being masculine?

Words ending in -e can be either masculine or feminine, so you have to learn the gender with the word. However, in this sentence, the masculine word for "the" (el) gives away that restaurante is masculine.

Does ahora have to go at the very end of the sentence?

No, Spanish word order is quite flexible. You can also say Ahora el restaurante está cerrado and it sounds perfectly natural.