This method gets the value of a user state variable and sets it in the session. This is the same as the method in \JApplication except that this also can optionally force you back to the first page when a filter has changed.
It is a method to add a model to the view. Joomla supports a multiple-model single view system by which models are referenced by classname. A caveat to the classname referencing is that any classname prepended by \JModel will be referenced by the name without \JModel. For example, \JModelCategory is just Category.