Better Windows Programming: Docking

If you set a control dock property to left, the control fill the left side of the form with a fixed length you set.

If you set a control dock property to top, the control fill the top side of the form with a fixed hight you set.

If you set a control dock property to fill and there is no control on the form, the control completely covers the form.

Next Recommended Reading Better Windows Programming: NotifyIcon