If the blower motor itself works but no hot air comes out the air ducts ensure the engine running temperature is correct, after ten minutes running the temperature gauge should be right in the middle of the gauge, if it is only 20 - 25% up the gauge the thermostat is stuck open. If the temperature is OK then locate the heater valve and get someone to operate the heater controls for you see that the valve moves fully open allowing the maximum amount of coolant from the engine to the heater core. I that is operational it is possible that the heater core is restricted with debris. With the heater valve fully open the two heater hoses at the firewall should be the same temperature if not coolant is not flowing through the heater core. First check the obvious, if the coolant level is low the heater core is often the highest point of the cooling system and may have air in it, top up the cooling system as required.