App design question

I want to know what is the best way to manage the creation and destruction of forms in an application. For instance if theres an MDI application in which froms are shown on menu clicks using a form object variable, what is the best way to make sure they are destroyed so that memory and resources can be reclaimed, once they are not needed any more or in the event of the application shutting down.

Any help with code snippets and reasons behind following a certain way of doing things would be appreciated!

i don't know if this is what ur looking for but i've seen people post the following or sort of the following to free up the resources ur program was taking

in the unload event they put:

set = nothing

or something like that ... i'm not really sure