This tutorial follows on from the pawn tutorial, showing extra techniques needed to make the bishop.
Extruding perpendicularly outwards or inwards is demonstrated.
The method used to create the groove is applying the Boolean modifier. The mesh that results from the Boolean modifier is usually a mess and for this reason many modellers avoid using it. The alternatives are much more involved and require high skill and knowledge levels. With the use another modifier (Edge Split modifier) the Boolean modifier can be used to give good results.