The WebPartManager control is required on every Web Parts page. Although never visible, this control has the critical task of coordinating all Web Parts controls on a page. For example, it tracks all the individual Web Parts controls. It manages Web Parts zones (regions that contain Web Parts controls on a page), and which controls are in which zones. It also tracks and controls the different display modes a page can be in, such as browse, connect, edit, or catalog mode, and whether personalization changes apply to all users or to individual users. Finally, it initiates and tracks connections and communication between Web Parts controls.
To add a WebPartManager control to a page
Drag the WebPartManager control from the Toolbox panel to your page.
Many ASP.NET controls do not have a visual representation at run time. The control is always visible in Code view. If you do not see a representation of the control in Design view, click Visual Aids on the View menu, and then click ASP.NET Non Visual Controls.
For a full description of all WebPartManager control properties, see WebPartManager Properties in the MSDN library.