1. With a noun compliment. This includes names of profession. Eg: It was an Earthquake.
2. The form an is used before words begining with A vowels(A,E,I,O,U) or words begining with A mute H. Eg: An apple, an Island
3. Used before a word beginning with a consonant, or a vowel with a consonant sound. Eg: A man, a hat , a University, etc......
4. Indefinite Article
4.1. A
4.1.1. With a certain numbers Eg: A ten, a hundred, a thousand
4.1.2. In exclamations before singular, countable nouns. Eg: such a long queue! , Such a long queues!
4.1.3. Used before a singular noun which is countable when it is mentioned for the first time and represent no particular person. Eg: I need a passport, They live in a apartment.
4.1.4. In expressions of price, speed, ratio, etc...... Eg: 30rs per kilo, 5 times a week
4.2. An
5. Zero Article
5.1. Before proper nouns Eg: I met David at kwality last night
6. Before abstract noun which indicates a concept or quality. Eg: Honesty is the best policy.
7. Definite Article
7.1. Used before singular or plural noun Eg: The girl is playing The girls are playing
7.2. The
7.2.1. The object or group of objects is unique or considered to be unique. Eg: The land, the sea, the sky
7.2.1.1. Before a noun which has become a Definite as a result of being mentioned a second time. Eg: His car got struck a tree, you can still see the mark on the tree.
7.2.1.2. Before superlative, first, second, etc ..... Used as adjectives or pronouns or only Eg: The first day(week) is the best day the only way
7.2.2. Before a noun which by reason of locality which can represent only one particular thing . Eg: Ann is in the garden (the garden this house)
7.2.3. Before the names of Holy Books Eg: The Bible