Click to select a single key. Selecting a key deselects all other selected keys. The Curves view displays the selected key with its tangents.
The Curves view provides the following methods for selecting keys:
Hold Command/Control and click to select discontiguous keys. Hold Command/Control and click a selected key to deselect it.
Click and drag on an empty spot in the Curves view to draw a selection rectangle. This selects all keys within the rectangle. Hold down Shift while drawing the selection rectangle to add keys to the current selection.
Double-click a selected key to select all keys on the same animation curve.