in your codebehind.cs go to Button1_Click event inside it..
add code as...
sds.selectcommand="SELECT [pcode], [fyyear], [date], [salary], [ta], [contigency], [nrc], [institcharges], [others] FROM [monthly] WHERE ([pcode] = "+DropDownList1.selectedvalue.tostring()+") and ([fyyear]="+DropDownList2.selectedvalue.tostring()+")";
because when u edit the selectcommand it automatically populates the sqlds..and databind it..following databind the gridview..
sds.databind();
grid.databind();
it works..but one thing google it properly..u'll find no of examples..