1. The Preview Bar performs a brief preview animation using the preset you are hovering your mouse on.
2. The Copy Button stores the data from the selected keyframes.
3. The Ease Button takes the easing curves previously stored by the Copy button, and applies them to a set of selected keyframes. Read more…
4. The Value Button takes the values previously stored by the Copy button, and applies them to a set of selected keyframes. Read more…
5. The Linearize Button turns the selected keyframes spatial interpolation into linear. Read more…
6. The Plus Button toggles between the Simple Presets library and the Complex Presets library.
7. The Preset Library. Read more…
8. The Speed Pass toggle switch auto adjusts the outgoing speed of a keyframe to improve smoothness when needed. Read more…
9. The Info Bar displays some useful information such as the name of a preset and the influence values of your copied keyframes.
10. The Continuous Time Interpolation Button converts the selected keyframes Time Interpolation to Continuous.

Hover your mouse over any main button to see some useful information: