Hi Samy,
If you're talking about the shoulder in particular then it depends on the character and the level of detail you are after.
Most of the time you can just create 1 single bone for the shoulder. But if you need more realism because you're showing the skin and muscles etc - then you would need to create a bigger mechanism. Maybe a bone that stretches the pectoral muscles and/or one that works on the lats and scapula.
There might even be a bunch of muscles under the mesh of the skin that push it around. That type of hyper realism isn't in my wheelhouse though.
Hope that makes sense.