how do I populate a combo with data form a database?

SqlConnection scon = new SqlConnection("your connection string");
           scon.Open();
           DataTable dt = new DataTable();
           string query = "Select ColumnName from TableName";
           SqlCommand cmd = new SqlCommand(query, scon);
           SqlDataAdapter sda = new SqlDataAdapter(cmd);
           sda.Fill(dt);
           scon.Close();
           yourComboboxName.DisplayMember = "ColumnName";
           yourComboboxName.DataSource = dt;