When you learn a new word that is a noun, learn the gender of the word as a part of the word by including a definite or indefinite article.
In English, only one definite article is used to represent a specific, definite object. The definite article the can be used in front of any noun without regard to gender: the girl, the book, the man, the chair. In Spanish, the definite article reflects the gender of the word that follows. The definite article el (the, masculine) is used in front of a masculine noun, and the definite article la (the, feminine) is used in front of a feminine noun.
In the following list, you can tell which nouns are feminine words because they are preceded by the definite article la, and you can tell which are masculine nouns because they are preceded by the definite article el
There is a masculine and feminine version of indefinite articles, which demonstrate the gender of the noun that they precede. While a definite article is very specific, an indefinite article refers to a less‐specific object. In English the indefinite article is the word a. When you request “a book” you are being much less specific than when you request “the book.” In Spanish, the indefinite article for a masculine noun is un, and the indefinite article for a feminine noun is una.
It doesn't matter whether you choose to learn el hombre or un hombre as long as placing el or un in front of the noun helps you remember that the word is masculine. La or una helps you remember that the word that follows is a feminine word. Later on, you will care about whether you want to say “a man” or “the man,” but for now, the articles are simply there to help you remember the gender of a noun.