The camber determines the curvature of an aerofoil. The thickness is measured from the top surface to the bottom surface at the point of maximum thickness.
The relative thickness is the “thickness/chord ratio” (t/c ratio) and is the maximum thickness of the aerofoil expressed as a percentage of the chord.
If you have a wing of say 8% t/c ratio and it has a chord of say 10 feet then the point of maximum thickness will be 9.6 inches. (8 x 120 / 100 = 9.6)