Use single-click curve editing

By default, the Move Nearest Picked Key Tool lets you single-click and drag to adjust tangent handles and keys on a selected curve. You can also set the tool to enable single-click editing for all curves (regardless of whether they are selected).

To allow single-click manipulation for all curves

Double-click the Move Nearest Picked Key Tool icon () to open the settings.
Turn off the Selected only option.
When Selected only is on, single-click editing works on selected curves. When off, you can single-click to edit all curves.

Tip

If you want to use a single-click tangent editing workflow, set tangent handles to always display by selecting View > Tangents > Always from the Graph Editor menu bar.

To allow single-click manipulation for selected keys on a curve

In the Preferences window (Window > Settings/Preferences > Preferences), select the Animation category (under Settings) and find the Graph Editor preferences.
Ensure the Left Mouse Button Alters Selections preference is enabled. (This preference is on by default.)
When this preference is enabled, you can move a selected key with a single click and drag.