masculine and feminine in Spanish
How do you know when something is masculine or feminine in Spanish?
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