We know that all people have gender, but in Spanish all nouns have gender. This means that every word for a person, place, thing or idea is either masculine or feminine. This can be confusing, especially when some words, like persona (person), can refer to a person that is man or a woman.
Why is it important to know if a noun is feminine or masculine? Because the gender of the noun changes the article or adjective that you can use with the noun. Masculine nouns are used with articles like el or un and have adjectives that end in -o, while female nouns use the articles la or una and have adjectives that end in -a.
To know if a noun is masculine or feminine, you should look to see what letter(s) the word ends with.