You could have googled
try this simple code..
DataTable dt = new DataTable();
string connectionString = "your connetion string";
SqlConnection con = new SqlConnection(connectionString);
SqlDataAdapter adapter = new SqlDataAdapter("SELECT DisplayNameColumn,ValueNameColumn FROM TableName", con);
adapter.Fill(dt);
DropDownList1.DataTextField = "DisplayNameColumn";
DropDownList1.DataValueField = "ValueNameColumn";
DropDownList1.DataSource = dt;
DropDownList1.DataBind();
check this link:
binding dropdownlist[
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