Masculine and Feminine Nouns
In Spanish all nouns are masculine or feminine. Usually, nouns that end with an "o" are masculine, and nouns that end with an "a" are feminine. For example, "manzana" (apple) is feminine and "diario" (newspaper) is masculine.
The articles "el" and "un" are used with masculine nouns, and the articles "la" and "una" are used with feminine nouns. "The apple" is "la manzana" and "a newspaper" is "un diario.