This document introduces the basic steps for creating a 3D part in CATIA: 1) Start a new part file and select the xy plane to sketch in. 2) Use the sketching tools to draw 2D profiles like squares and constrain dimensions. 3) Exit the sketcher to enter the 3D environment where the 2D profile takes on an isometric orientation. 4) Use tools like pad to extrude the 2D profile into a 3D solid part.