If the spell mastery ability applies, and you find three basic Forest cards, one of them will be put onto the battlefield tapped and two of them will be put into your hand.

Check to see if there are two or more instant and/or sorcery cards in your graveyard as the spell resolves to determine whether the spell mastery ability applies. The spell itself won’t count because it’s still on the stack as you make this check.

If you only find one basic Forest card, you’ll put it onto the battlefield tapped. You won’t be able to put it into your hand, even if you want to.