The difference is quite small. Use the word "unos" when you want to emphasise who they are. And "varios" when you want to focus only in the quantity of them. For example: Q: ¿Vas a ir al cine sólo? - If you answer is : No, voy a ir con varios amigos (you are saying: I'm not going to go alone.) If you answer is: No, voy a ir con unos amigos. (you are saying:" I'm going to go with people that I know, but I don't give more information about them. Basically it is a way to "name" them, that's all. I think it's similar in English: I'll go to the cinema with several friends I'll go to the cinema with some friends Hope It helps

Unos = a few Varios = many Unos amigos = A few friends Varios amigos = many friends it's a matter of quanitity

Unos amigos = Some friends. Varios amigos = Several friends. El significado es muy similar.