Gender indicates whether the pronoun refers to a word that is masculine (for males), feminine (for females), or neuter (neither males nor females).

Masculine Feminine Neuter
He, him, his She, her, hers It, its

When using pronouns, you must avoid shifts in person and gender.

Shift in person Juan is joining the high school band because you will get a scholarship for it.
Correct Juan is joining the high school band because he will get a scholarship for it.
Shift in gender The dog wagged its tail because he was happy to see me.
Correct The dog wagged its tail because it was happy to see me.