Many people have doubt about when to use definite articles and when to use indefinite articles.
To clear this doubt we should know the difference between these two types of articles.
Indefinite articles are used when you are not talking about something specific or certain.
Ex: Give me a ball.
Whereas definite article is used when you are talking about something specific or certain.
Ex: Give me the red ball.
Above examples show that we are talking about specific thing which is red ball. Whereas in the example of indefinite article, we are talking about ball which can be of any colour.