Easy, put the valve stem into the rim first with the nut half way on just to stop it disappearing back into the tyre.
You leave the tube out, put the tyre over the rim where the valve is, using some soapy water and a rubber hammer put the underside of the tyre on, that's it, then with some baby power put the tube inside the tyre, inflate the tube a bee's dick then rubber hammer and soapy water the tyre on.