I would like to know how you should write website pages that use for example 3 models and several actions on them.
Because there is usually only a controller involved with a page call and only a special action.
For example:
there should be a page which displays a group of people, and on that page I can edit the peoples names and assign new people to the group and i can add people as new managers of a group.
Does this page need its own controller or how do I program such pages?
Actions can belong only to controllers. In each action you can work with any models of your application. In your case you must create a UserController and a list of actions (e.g. actionViewList, actionEdit, actionAssignToGroup).
Check this for more information: Yii Controller