what is diference between webpage and webform?

The difference is conceptual. "Webpage" is the page itself, with the HTML or XHTML code itself along with all the style sheets, browser scripts, images and so forth. "Webform" means the input and associated elements inside a <form> tag when talking about X/HTML coding in general, or the layout and design of page elements when talking about ASP.Net and Silverlight. This second context is to make a distinction with "Windows forms", which is the layout and design of Windows forms.

from my side , i think that web forrm is a special dotnet web page where we can add .net controls and classes to play with , such as listview and treeview are kind of controls ready-to-use we can add to web page in design mode ... a web page is always a standard web page that we cannot use .net controls like web forms but in order to use controles like treeview we have to call javascript libraries that can show for us some data grids and data treeview and some javascript toolbars where these controls are not .net controls but web controls ... these ones are made in separated projects by other web comunities and companies and are downloadable for free as open source or available for sell