PartDesign Pocket

Introduction
'Create a pocket with the selected sketch' - This tool takes a selected sketch as its input, and produces with it a 'pocket'. A pocket is essentially an extrusion of a sketch that subtracts from the geometry it protrudes into. For example, if a sketch were made simply of one circle on one face of a cube, then the pocket formed by that sketch would manifest as a hole 'drilled' into the cube:

Parameters
Pocket has one parameter:

Length - the distance the sketch will be extruded to create the pocket. A sketch will extrude in a direction normal to the sketch plane or face on which it resides.