A and an are indefinite articles that are used to identify nouns. They are non-specific and can refer to any member of a group.
Here are some examples:
- My sister is buying a car.
- My brother went out to buy an apple.
A and an can only be used with singular nouns. You shouldn't use them with plural nouns.
If you are using a plural noun, you will either need to change the article to 'the' or specify the number of items:
- I bought the magazines.
- I bought two magazines.