"Our elephants are not white."
Translation:Nuestros elefantes no son blancos.
nosotros is a subject pronoun corresponding to the English "we". In Spanish, it can include a group of males or a mixed group of females and males. If "we" are all females, we would use nosotras.
nuestro/nuestra/nuestros/nuestras aré possessive adjectives corresponding to the English "our".
In English, we have only one "our", just as we have only one "red". We can have a red book or a red shirt or red shoes or red tables. But in Spanish, the adjectives must agree with the nouns they are modifying/describing. Thus we have libro rojo, camisa roja, zapatos rojos, mesas rojas: four different words for red.
The same with "our" -- remember it is an adjective and must match the noun it modifies/describes, not the subject of the sentence: nuestro libro, nuestra camisa, nuestros zapatos, nuestras mesas. It doesn't matter whether these items are owned by males or females; this is about grammatical gender of the noun.
[Not to over-complicate things, but because it will come up, I should add that nuestro/nuestra/nuestros/nuestras are also possessive pronouns corresponding to the English "ours":
Q: "Whose books are these." = De quién son estos libros?
A: "Ours" --> Nuestros]
As a matter of fact, you can say: "Nuestras elefantas no son blancas", but you can't say it in the form you wrote it. I'll explain you. In this case, you're starting with a plural female possessive adjective (Nuestras), so the noun that comes next to it should be both, a female and a plural noun (elefantas). Finally, the last adjective has to be as the noun: female and in plural (blancas).
"Nuestras elefantas no son blancas."
In masculine, it would be the same thing: "Nuestros elefantes no son blancos."
PD: That's a really uncommon phrase in Spanish (the female one), but still can be used. :)
The subject of the sentence is elefantes and the corresponding conjugation (form) of the verb ser is son -- third person plural, "(they) are"
eres is the tú (familiar you) conjugation of the verb ser
In English, we don't have as many different conjugations (which is a reason why we need to have explicit subjects). But, think about how strange it sounds to say "I is" or "you am"; they (subjects and verb forms) don't go together.
Grr, elephants have gender too... this gender thing is the most frustrating part of learning Spanish. Things have gender, animals have genders seemingly randomly (some do some don't), colors have genders randomly (some do some don't).
Anyway, was not taught elefantas before this. It just randomly popped up in Strengthen Skills part without it being in any lesson..