You must use [existingView addSubview:newView];to add a view to an existing view. newView will appear on top of the existing one. Thus, conceptually, you would create a button on an existing screen, connect it to IBAction, which calls this method:
CGRect newSize = CGRectMake(0.0f ,0.0f, 320.f, 400.0f);
UIView *newView = [[UIView alloc] initWithFrame:newSize];
[existingView addSubview:newView];
[newView release];
newView .