Basic - Remember the articles

The undefined article A is used before words started for consonants.Look at the exemple:

A teacher
A car
A motorcycle

The undefined article An is used before words started for vowels. Look at the exemple:

An apple
An eraser
An artist

There's some exceptions in that rule, let's learn a little bit about them:

When the word is started for 'U' and it sounds like 'IU' we use the article A.

A University
A Unit
A Universe
A Unique

When the word is started for 'H' and it doesn't have any sound and the other letter is a vowel, we use AN.

An Hour
An Honour
An Honest