"A spider is an animal."
Translation:עכביש הוא חיה.
who "they"? Hebrews don't have equivalent for it, just he/she according to grammar gender of the noun. That's why there are 2 options 1) הוא/היא ;2) זה. both mean pretty much the same, though there is a slight difference in meaning. 1) smth1, he/she [is] smth2; 2) smth1, this [is] smth2.
Anyhow, both play a role of copula, between 2 nouns, as smb has mentioned above