masculine and feminine in Spanish
How do you know when something is masculine or feminine in Spanish?
For nouns without a sexual gender you have to learn each gender individually although many nouns give you a hint e.g nouns ending in o are masculine and those ending in a are feminine but there are exceptions to the rule.
Unfortunately you have no choice but to memorize every word. There are guidelines, but there are exceptions to the guidelines. You'll get the hang of it though, I promise!
Feminine endings tend to be -a, -ion, -ad, -triz, -umbre (e.g. la chica, la reunión, la ciudad, la actriz, la costumbre) and masculine endings tend to be -o, -ama, -ema (e.g. el chico, el panorama, el tema). Numbers, days, and months are also all masculine.
Here's a pretty decent summary: https://www.e-spanyol.hu/en/grammar/gender.php
Short rules: people and animals according sex or gender, the rest of the words, according to their endings (mostly -o for masculine and -a for feminine). We native speakers learn them one by one, through mistakes ;)