A quick simple example, i have not yet played with anything advanced, but this should be enough to get you started.
After enabling the Bsurface addon
Press N to bring the panel to the 3D view right, then Click on New Layer in the Grease Pencil tab
Then click on the “Surface” button
Hold the D key and draw, the pencil drawing should be projected on the surface of the object.
Once you have made a few strokes, in the T panel (the panel to your 3D view left) , click on “Add Surfaces”
After that, tweak the settings in the Operator tab (or press F6 to make the Operator tab appear as a popup)
You should have no need to enable the snap tool in the bottom of the 3DView
The GPL version is much older and i remember it had lots of problems, do not use it and do not enable it in your Addon panel (as it could create conflicts i guess), enable and use only the new BSurface addon from there : http://www.bsurfaces.info/
Hopefully in next version of Blender, the GPL version will be removed and replaced by the new BSurfaces.