By IsCrossPostback Property we can send values to the next
page..
Exam::
Let There Are 2 Page page1.aspx & page2.aspx.....I wanna
send value of a textbox from page1 to page2.
Step 1::
  In aspx of page1,
   <div>
   <asp:TextBox ID="Textbox1"......></asp:TextBox>
   <asp:Button ID="Button1"....postbackurl="~page2.aspx"/>
    </div>
Step2::

  In Pageload() of page2.aspx

pageload()
   {
    if(PreviousPage!=null && PreviousPage.IsCrossPostBack)
      {
       TextBox text=PreviousPage.FindControl("Textbox1")
                                               as TextBox;
        if(text!=null)
         {
          Label1.Text=text.Text;
         }
      }

   }

   .........Here Label1 is a label of page2.Where i show the
value of 1st page's text box value....