The markup of a page in Visual Studio contains the raw and unprocessed source for the page, including the HTML, ASP.NET Server Controls, and programming code. The web server then processes the page and sends out the final HTML to the browser. In the browser this HTML is then used to render the user interface.
The easiest way to store HTML fragments that you use often is to select them in the Document Window and then drag them to a free space on the Toolbox. When the item is added, you can rename it to a more meaningful name. Now you can simply double-click an item or drag it from the Toolbox into your page whenever you need it.
You have a number of ways to reset part of the customization changes you may have made, including:
To change the property of a control on a page, you can click the control in Design or Markup View and then use the Properties Grid (which you can bring up by pressing F4) to change the value of the property. Alternatively, you can change the property directly in Markup View.