Bodies are the fundamental objects in the physics scene, but they are not what you actually see bouncing around and colliding with each other.
You can think of a body as the properties of an object that you cannot see (draw) or touch (collide with). Some of these invisible properties are:
First Select body creation tool from objects toolbar, by pressing corresponding toll with left mouse click.
Now bodies can be added to the simulation by simple drag and draw with mouse on canvas. If Grid is on then mouse pointer will be snapped to closest grid point.
adding body with mouse screen-shot
Note that tool automatically resets to move-tool after creation of body.
Bodies can be removed in four ways (other than by starting a new simulation):
select-bodies body in canvas by clicking with mouse and press delete to remove body from simulation.
Select delete tool and click over object to remove, or create rectangle by dragging to remove all enclosed objects
By selecting the Remove option from the Body context menu.