How would you use article in a sentence?

If you mean the Word article:

The article of clothing looked old.

I read an article in the newspaper.

If you mean article of speech, those Words called Articles of Speech are a, an, and the.

A teacher told me to be quiet. (No particular teacher, just "a" teacher.)

The teacher told me to be quiet. (The indicates one specific teacher.)

A is used when the next Word does not start with a vowel.

An is used when the next Word starts with a vowel.

I saw a shark. (A is used when there's no exact one; it could have been any shark.)

I saw an octopus. (An - just something random that starts with a vowel.)

I saw the shark. (Meaning one particular shark, such as at Sea World.)

I saw the octopus. (Meaning one particular octopus, such as at Sea World.)