Beforehand, you must :

     select PartDesign WB,

PartDesign is a workbench that allows you to represent a solid starting from a block of material that will be modified sequentially until the desired final shape is obtained.

Each operation adds or removes material : we say that the construction is cumulative.

     create a new document,

     then create a body.

A body is a container specific to PartDesign which contains a single and contiguous solid (in a single block, but this is no longer obligatory). It associates an origin with this solid as well as standard axes and planes.

A body must be active (in this case it is displayed in bold characters) in order to be able to be supplemented with various functionalities (if this is not the case, double click on its name to make it active).

Construction technique :

The current construction technique relies in part on a sequential (repetitive) cycle which can be described by the following graphic.

Note :

If you are inexperienced, it is advisable to consult the preparation of CAD work page.