The upper level, where you begin, is really just a training area. It's to get you introduced to the Mommy Bird, and starting to figure out how to move around.

First off, go up the corkscrew plant to the next level. You get to see the mommy bird and the baby through a close-view plant. OK, go around the other side up to the top. You'll meet the plant that uses its leaves to block the sun. Poke it so it lets the sun through. Now the sun shines on the other plant, the light-redirector one.

Point the light redirector down at the pod next to the dried-up corkscrew plant. It'll burst the pod, giving the corkscrew plant some water. Now you have a way of getting down into the middle regions.

The Myst 3: Exile Walkthrough