How is friction applied?

Friction is applied, by making the surface of whatever you want to slide across it (the thing you want to apply friction to) is really rough. You can inscrease, and decrease the amount of friction acting on an object by changing the texture, material and smoothness of the surface. Smoother surfaces don't apply much friction to objects, and rougher surfaces apply a lot. An example of this, is Wellington Boots. They have rough underneaths, so you don't fall over - they apply a lot of friction.