A. Article
1. An article is a word as a determiner that indicates definiteness of a noun as general (indefinite article: ‘a’ or ‘an’) or specific (definite article: ‘the’).
2. Indefinite Article: 'a' or 'an' 
3. Definite Article: 'the'

B. Indefinite Article: 'a' or 'an'
1. Use Indefinite Article: 'a' or 'an'
2. Do not use Indefinite Article: 'a' or 'an'

C. Definite Article 'the':
1. Use the Definite Article 'the'
2. Do not normally use the Definite Article 'the'