The warm rent (Warmmiete) is your total monthly rent. It includes your cold rent (Kaltmiete) and utilities (Nebenkosten). It might not include electricity for your lights and appliances.
Cold rent (Kaltmiete) + utilities (Nebenkosten) = warm rent (Warmmiete)
Your warm rent is adjusted every year, because your utility costs (Nebenkosten) can change based on your usage.