Theory
Surface area means the total area covering the outside of a 3D shape. Imagine wrapping the shape in paper: the amount of paper needed is the surface area.
Surface area is not volume. Volume fills the inside and uses cubic units such as cm³. Surface area covers the outside and uses square units such as cm².
A reliable method is to draw or imagine the net, then find the area of each outside face and add them.
For a cuboid, there are three different face pairs: length x width, length x height, and width x height. Each pair appears twice.
For any prism, find the two matching end faces, then add the rectangles that go around the sides.
For a cylinder, the two circular ends have total area 2πr². The curved face opens into a rectangle with width equal to the circumference 2πr and height h, so its area is 2πrh.
In Edexcel questions, diagrams may hide one face or give a compound solid. Mark the faces carefully so you do not count one twice or miss one.