ToolTip control may be attached to some ASP.NET controls and displays information for the related controls.

Specify how the ToolTip opens - with a click on a Help button, with a click on the related page element (e.g. a TextBox, TextArea, DropDown, Button or any other control that has onFocus and onBlur client side events), by pressing the F1 key - set AssociatedControlID value, or when the pointer rolls over the Help button.

ToolTip is not designed to provide a single help button for each page, it is designed to provide help for each form element. This is true, fine-grained context sensitive help.