Is your furnace gas or electric?
If electric, do you have a heat pump?
It could be several things. Let's start with the easy stuff.
Check in your breaker panel to see if the breaker for the heating elements in your furnace has opened. If it has, click it first to off and then to on.
Then go to your thermostat and turn it up to call for heat.
Let me know if you have done that and tell me what happens.
OK. So no hot air.
It could be several things that will all require opening up the heating unit and checking.
The elements could be burned out.The high limit thermostat could be bad.The circuit board that controls heating and cooling could be bad - possibly a relay but I have seen the boards have blown components.
Are you capable of checking the furnace out or will you be calling in an HVAC person?