we use an wehen the word after starts with : a e o i u examples: - an old man - an important thing we use a when the word after starts with the other letters example : - a chinese man - a beautiful day

As general rule, always put "a"or "the" before a noun (or before the adjective before the noun). It is better to use too many "a"or "the" than none at all.

"The" is used usually to specify a specific noun, such as "the ball". It means there is a certain entity that is distinct from another entity, like "the green ball". If you were to say "a green ball" that would not specify which one you're talking about. "The" is called the 'definite article' in English and 'a/an' are indefinite articles, because they do not define a specific noun. So whenever you are deciding which article to use, ask yourself 'Am I referring to a specific thing, or could this be anything?' For instance: "I am the one you've been looking for" is very specific, so it takes 'the'. But "I am a language learner" means you are one of many language learners =) Hope that helps