The importance of gender to Spanish grammar is that as a general rule, adjectives must be in a masculine form when they refer to masculine nouns and in a feminine form when they refer to feminine nouns. The masculine definite article (el or los for "the") is also used with masculine nouns and a feminine article (la or las for "the") is used with feminine nouns. Also, masculine pronouns are used when referring to nouns that are of masculine gender, and feminine pronouns when referring to nouns that are of feminine gender. Neuter pronouns are used to refer to unspecified nouns or nouns whose gender isn't known, as in "¿Qué es eso?" for "What is that?" (eso is neuter).
Adjectives don't always vary according to gender; for many adjectives, the masculine and feminine forms are identical. Neuter adjectives are used infrequently, but where they are used they have the same form as the masculine form and are thus indistinguishable from them.
The division of nouns into masculine and feminine genders is somewhat arbitrary. Nouns that naturally refer to males (such as el hombre, "the man") are typically masculine, and nouns that refer to females (such as la muchacha, "the girl") are feminine. However, the gender of other words is usually unpredictable. Although there are many exceptions, it is common for nouns that end in -o to be masculine and those ending in -a to be feminine.
Example of Spanish sentences using feminine words: Mi prima es flaca. Ella tiene dos camisas. (My cousin is skinny. She has two shirts.)
Example of Spanish sentences using neuter words: Lo bello es caro. No comprendo esto. (That which is beautiful is expensive. I do not understand this.)
