How to get data into gridview by selecting dropdownlist

Hi, I was created a web page that contains 3 labels with textbox 1 button control 1 dropdownlist and 1 grid view. Initially using 3labels, text boxes and button I was inserted data in database with the help of ADO.Net(Sql Data Reader). I was loaded data in dropdownlist list. But when I am not able to get data into gridview by selecting dropdownlist. Can anyone give solution for this problem. Note: This question is asked in System Test of interview round which I was faced.