How do you create a custom event? is it possible?

I have a form
it creates an instance of another class
this class file has a public property which is of type bool

everytime that bool value changes, i want the form to pick it up (the change) and notify me. is it possible?

If it is possible, then the "notification" event can be done on the form? or must it be done in the class the variable/eventhandler is created?