For doing the thing @codewiz describes: https://www.youtube.com/watch?v=iy9amRGcCCA
Once you're somewhat familiar with "Part Design" and Sketcher, I recommend getting familiar with the "Part"-workbench and boolean operations (can't remember which tutorials I found useful for this atm).
If the goal is to 3D-print your model, you also need the tool "convert shape to mesh" from the mesh workbench.