Use the if a reader could identify the noun specifically.
- Please turn off the lights. We’re not going to the museum tomorrow. (Count)
- The food throughout Korea is excellent (Non-count)
Use a/an if the noun refers to a single item that is not specific. Never use a/an with plural or non-count nouns.
Bring an eraser to class. You’ll be using a pencil to write an essay today. (Count)
Use a quantifier such as enough, many, some, etc. if the noun represents and unspecified amount and that amount is more than one but not all.
- Amanda showed us some souvenirs of her trip to New Orleans. Many birds go there in the summer. (Count)
- We didn’t get enough snow this winter.
Use no article if the noun represents all items in a category or the category in general.
- Teachers can attend the game for free. Actors must report backstage by 5:00 p.m. (Count)
- Gold is a natural resource.