After selecting a stroke/shape using the stroke/shape list or one of the Select tools, you can edit and animate its attributes in the properties panel. For more information on selecting strokes/shapes, see Selecting Existing Strokes/Shapes for Editing and Working with the Stroke/Shape List.
If you want to edit the attributes of a stroke/shape prior to drawing one, you should do that in the RotoPaint tool settings in the Viewer. (See Working with the Toolbars.)