Can one work with textboxes etc from a class other than the form of which the textbox is a part?

the scenario is as follows. if one has a form then any method or function on that form can work with a textbox or something located on that form. but i have created another class as a screen manager and i have found that this class cannot work with the textboxes. am i doing something wrong or is it just impossible to work with textboxes or any controls from another class?

You can, just change the access modifier of those controls to public