Move the stud finder across the ceiling until it beeps, noting the presence of a joist. Mark the location of the ceiling joists in the area where you plan to install the recessed light fixture with painter's tape.
Select a location along the sloped ceiling for the recessed light. You can install the light fixture wherever you wish provided you do not try to install the light over an existing ceiling joist.
Place the housing template against the ceiling. Trace around the lighting template with a pencil.
Score the traced outline with a utility knife. Cut around the traced outline's edges with a drywall saw.
Remove the cut-out section of ceiling tile or drywall. The hole left behind in your sloped ceiling will house your recessed lighting fixture.