My friends and I were playing and someone cast a Silverglade Elemental and used it's ability to bring a Verdent Force into play I told him that he could only bring forst LANDS, not any green card, into play. Is this correct?
Yes. I forest is just that - a card named 'forest' (occasional older cards vary this rule slightly, but It'll do for an answer). A card with green mana symbols in the top is NOT a forest. Remind your friend: Not all lands which produce green are forests, either.