Answer:
Because the gender of the noun helps you to know if you have to put el or la.. For example, LA comida or LOS escritorios. As you can see, comida ends with an a, so you can tell that it is feminine. Therefore you would put la to go with it. The same goes for escritirios. It ends with an os so you would put los because it is masculine. And don't forget the ending with the os is only for plurals! If you have a singular noun such as carro, you would put el since its masculine and singular.
Explanation:
Hope this helps!! If you have any questions, just comment and I will explain :)