The first step would be to sketch out your idea on paper. Once you have an idea, start with a rectangle and extrude it from the center point of the rectangle.
Step1. Clicking the Extrude Boss or Revolved Boss/Base.
Srep2. Draw the one of the three plane (Front plane , Top plane, Back Plane).And Then the display on the Tools.
Step3. Create a draw and with the help of the entity tool or select tool on the sketch toolbar and create a draw a figure.