Warp to the Faron Woods Entry Bird Statue upon arriving.
Once you land, go east and across the gap by swinging with the rope. On the other side, go along the fairly linear path to the mushroom-filled area, using the shortcut if possible. Around here, go along the northern portion of the area and you’ll find a rock blockade; Bomb it to find a Piece of Heart!
Afterwards, go east and up the slope, avoiding the Quadro Baba part-way up it. At the apex, continue going along the path and take a left turn. Continue up the hill ahead and follow the path to the Great Tree. You want to reach the northeastern temple ruins.
Around here, you’ll find a bunch of Blessed Butterflies surrounding a lit-up portion in the path. Go there and catch a Butterfly or two if you want (this kind of thing won’t affect anything), then take out your Goddess Harp. A scene is then triggered, with another circle of light expanding and contracting. Play the harp in time with it and, eventually, you’ll need to thrust your Goddess Sword into the circle – hold A and shove the Wii Remote down vertically (but not into the floor … or your crotch. >_
And so, you have found the Trial Gate, sending you to a new area…