Let's say we want to animate the tail of the Lion without moving the feet. To prevent the feet from moving we need to lock them.
Select the feet control points and Ctrl click with left mouse button anywhere in the work space.
Now we can move the tail without disturbing the position of the feet.
To unlock the points, first deselect all points by clicking at an empty place in the work space. Then Ctrl click again with left mouse button.
If you have selected points they will get locked too.
You can also use the action "Unlock Points" at the left side.