How to fill dropdownlist from database.

Hi,
        I am beginner for Asp.Net. I don't know how to fill dropdownlist from database using c#.
I have created sqlconnectionstring in web.config:
<appSettings>
        <add key="connectionstring" value="user id=tcms;password=tcms; initial catalog=tcms; data source=10.160.1.4"/>
    </appSettings>
 how to fetch data's from table then fill dropdownlist.
I have searched from net but i can't understand. so tell me clearly anyone plz.
Thanks,
Kanchana.

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