Proper nouns (e.g. John, Alice and India) do not take articles.
- Incorrect: The John is my friend.
- Correct: John is my friend.
- Incorrect: The Tokyo is a big city.
- Correct: Tokyo is a big city.
A singular common noun (e.g. boy, cat, tree, book, apple etc.) must have an article.
- Incorrect: There is cat on roof.
- Correct: There is a cat on the roof.
A plural common noun cannot be used with the article a. It is usually used with no article, though some is sometimes used before it.
- A spider has eight legs.
- Spiders have eight legs.
Remember that a noun can be common in one sentence and proper in another sentence.
A superlative adjective is usually used with the.
- Incorrect: He is best player in the team.
- Correct: He is the best player in the team.