USE A/ AN- THE

•          We use a before words that start with a consonant sound: a book, a pencil, a car, a university
•        We use an before words that start with a vowel sound:  an apple, an eraser, an umbrela
•          We use a/an for something we mention for the first time. We use the for something we have already mentioned: This is a book. The book is anna´s.