When does a form.paint event occure?

Thanks a lot for the answer. I want my program to have 2 functions that recieve PaintEventArgs; One which will run once everytime the program starts and one which will run thrugh the whole time the program runs. I've defined the second one as OnPaint, and done a timer that does Invalidate() in every Tick, and it worls fine. Now I need to do the other function; the one which will run only once. How can I define a function like that? how can I send PaintEventArgs to a function myself, or how can I create a function like Invalidate which will send it? Or is there any other way to paint the screen, without using PaintEventArgs? thanks :)

Windows determines when to call this event. If you want to force repaint use: Refresh() - immediate repaint or Invalidate() - repaint in next event loop