Hi Richard, In the 3D view, select the two objects, go to the editor pull-down menu>3D Boolean>select the option and fidelity you want>click ok. To move the opening around, you will need to go into the Modeling room and lasso or marquee select the vertexes and polys you want to move and do it that way. Unfortunatly, the Assembly room doen't serve both modeler and assembly functions.