It depends what your walls are made of. If they are stone, brick or breeze blocks then it’s just the same as putting up a shelf, masonry drill, rawlplugs and big screws. If it’s an internal stud wall (knock it and see if it sounds hollow) you need to find the joists and wood screw it to those. Don’t under any circumstances screw it to the plasterboard or it will fall off and kill someone!