How to avoid page refresh on submit click in asp .net?

Practically it has many ways, but let me show you 1 way to do so. Here i am going to use Jquery.
First of all create JS function or Jquery function, which required to call on "OnClientClick". Than you have to call the Code Behind method for doing the database operations(If you have such method else create such).
Remember that the method should be

"[WebMethod]"

.
Let consider function name "JqueryFunc" for better understanding.

<script type="text/javascript">
function JqueryFunc(){
    // Validate your controls if required.
    // Now you need to call the code behind method such like below & pass required parameters
    // consider parameters as other controls data which you required to store in DB.
    PageMethods.SetAllValues(parameter1,parameter2);
}
</script>

Now consider that you have created method in code behind which takes parameters and do required operation in database.

 [WebMethod]
//Consider parameters as per your requirement
 public static void SetAllValues(int parameter1, int parameter2)
{
  //perform all required database operations here.
}

And now just call the JS function from the button.

// OnClientCode will have the JS function and return false.
<asp:button runat="server" id="btnFunc" text="Func" onclientclick="JqueryFunc(); return false;"></asp:button>

Hope this will help you.