Definition - Articles are words mostly used before nouns. In German, articles are the key to understand the gender of nouns because they are divided in three genders, just like nouns are.
Examples of German articles followed by nouns:
             • der Brief [the letter], eine Tasche [a bag], die Gläser [the glasses]

Types - There are two kinds of articles: definite and indefinite.

Definite articles are used to indicate specific nouns (e.g. the person of which we have already spoken in a speech, the thing about which we have already read in a written passage, etc.) The German definite articles are:
             • Singular masculine - der Brief [the letter]
             • Singular feminine - die Tasche [the bag]
             • Singular neuter - das Mädchen [the girl]
             • Plural for all genders - die Leute [the people]

Indefinite articles refer to nouns in a non-specific way. The German indefinite articles are:
             • Singular masculine - ein Tisch [a table]
             • Singular feminine - eine Zeitung [a newspaper]
             • Singular neuter - ein Glas [a glass]

Note: there is no plural form of the indefinite articles, neither in German nor in English.