PostBack URL question

Hello All,

    This is the first time I am using PostBack URL, I am not sure I doing it right, Can anyone guide me on how to the following please,

 

I have a button on my details page with the following code
onclick="backpagebtn_Click" PostBackUrl="~/Self_Assessment.aspx">Back to
Summary Page</asp:LinkButton>

 

I have a main page with a gridview and a dropdownlist. When the control returns to the main page(S ...