Come with 3 or sometimes 4 fixings. Telescopic, mark wall for space between the rails you wish to use, measure exactly centres of space between top rails and bottom one you wish to use. Mark wall same, drill, mount back of telescoping leg, insert other part, assemble wdgy bit onto it wth towel rail held in place, screw together, do up small screwes in side of telescoping leg to fix depth.
Mark floor exactly beneath valves (which are straight through for showers), bring pipe up to rad valves, tighten nut. Open valves, fill system, bleed towel rail. Pat yourself on back.