Passing Values to Class Files and back

Question

I`m a Win Forms newbie. How can I pass Control Object Values [Lets say Text Box Values] on a Windows forms to a Class File, and return values from the Class File to the main form.

This is what I`m doing - I have a main form, with a lot of text boxes, drop downs..etc and I want to pass values of them to a Class File [not another windows form] and do all my calculations using the methods there and return values back to the main form.

Different ways of doing this?

I have done this on web applications using query strings...and I just can`t figure out a way of doing this on windows forms...this is driving me mad.

Help will be greatly appreciated.

Thank You
San