Magnetic paint is applied to the wall or surface just like regular paint. The only difference is that the paint has tiny iron dust particles in the paint that makes it magnetic. The paint is a dark primer used under other paints that makes magnets stick to the wall or surface that has been painted. These paints need to be mixed well before using so that all the tiny iron particles are mixed thoroughly within the paint. When the paint has been sitting for a while, the paint should be stirred again so that each batch of the paint that is poured out has the iron mixed well in the paint.
Using a foam roller, the magnetic paint should be applied one layer at a time. It usually takes more then one layer of the primer to magnetize the surface. Each layer should be applied generously and left to dry for at least a couple of hours. Three coats of the paint are usually recommended to cover the area completely with the tiny iron particles. As much as six coats of the primer can be used in order to bring as much iron to the wall or surface as possible. The problem with applying more layers is that the iron particles seem to get further away from the surface. That is why allowing the layers to dry first before applying another layer is so important. The surface will end up being bumpy, but that is the iron coming to the surface of the wall.
Magnetic paint should not be combined with chalkboard paint. The iron particles in the paint would make it to rough of a surface to write on for a chalkboard and would make it to hard to clean. The pull force of paint is not as strong as a steel door but can hold papers of minor weights. There are many different kinds of magnets that can be used on a painted surface. The smaller magnets would not hold as much weight on a painted surface as it does on a steel door. Larger magnets will have larger areas touching the wall surface that will make the magnet work better at holding things up. Using larger magnets on painted surfaces, like the larger round discs will keep papers hung up longer. The discs come in many different colors, so they can be used to separate different items or subjects all on one wall or surface.
You may want to check out how House Turquoise use a magnetic primer under her chalkboard paint to have the best of both worlds.