Build the part with a shelf at the back
The three views below show a block with a shelf cut into its back half. Build it from the full block. Nothing about the shelf breaks the front view's outline, so its depth has to be read from the other two views.
The part, in three views
corner 1 of 4
Click a face to cut that block away. Right-click to put a block back. Use Turn left/right to walk around the part: a feature on the far side cannot be reached from here.