If you want to setup a physics data for an object that is already on the screen, just right-click on it and select “Edit Physics” button from drop down menu, this will bring up the “Edit Physics” dialog.
There you can choose if your object is static or dynamic, set its mass, friction, density and so on, and draw the polygon mesh for its fixture shape.
You can also right-click on an asset inside the right panel, and select “Edit Physics”.
If done so, later every time you drop this asset to the stage you will have physics data copied with it. It is also important to notice that physics data is not saved unless you click “Save Physics Data” inside the edit physics dialog. If you just close it, data is lost.