In Spanish, Adjectives must agree in Gender and Number with the Nouns they modify:
Notice that in the Spanish phrase EVERYTHING is Plural. That's rule #1. The other rule isn't so easy. In Spanish, nouns have Gender. They are either masculine or feminine. English doesn't have that, but the closest thing would be using a/an.
|English||A dog*||An apple*|
|Spanish||Un perro||Una manzana|
Okay, so Nouns have Gender. But since Adjectives have to Agree in Gender...
|English||a white dog*||An red apple*|
|Spanish||Un perro blanco||Una manzana roja|
Well, alright, I can accept that. But what if you have a situation with both issues at once? Gender AND Number?!
|Singular||a white dog*||An red apple*|
|Plural||Some white dogs||Some red apples|
|Singular||Un perro blanco||Una manzana roja|
|Plural||Unos perros blancos||Unas manzanas rojas|
Not difficult, just something to keep track of.
*These words aren't really masculine/feminine, but I used them to show you what I mean.