In general the sequence of operation,
1. Call for heat from the thermostat, there should be 24 volts on the thermostat connection in the unit. Measure between the C and W terminals.
2. When the thermostat calls for heat the inducer motor should start running. If it doesn't run, nothing else happens, just sits there looking stupid.
3. Inducer runs and closes a pressure switch, or sometimes a centrifugal switch on the inducer motor, I don't know which your unit has, but a pressure switch is more common. if the pressure switch fails, again, nothing else happens.
4. Pressure switch closes and then a not surface ignitor will glow. You will see it up by the burner. You might have spark ignition instead, again I don't know, but if you have spark ignition you should here it start arcing in the burner area.
5. Shortly after the ignitor starts the gas valve will open and the burner will light. There will be some method to prove flame, usually just a simple flame rod that extends into the burner flame.
6, If all this works, the blower fan starts. The blower fan might just time out to start, so it might start running after 15-30 seconds any way. If the blower fan does not run the unit will most likely run until the heat exchanger gets too hot and trips a thermal over load.
Speaking of overloads, often there are overloads around he burner, up to 3-4 of them on some units. Two wires going to them with a little red button. Some times they just trip. Make certain they are all reset, give each red button a firm push.
Common issues. Inducer motor seizes up over the summer and will not run. sometimes they can be forced to turn and will run, often they need to be replaced.
Hot surface ignitors fail. They are fragile and crack and/or burn out. Typically they run on 120 volts. If you can figure out the wires to the ignitor you can measure the voltage.
Sometimes the control board fails causing any of this to not function. It takes electrical testing to prove what has failed. Many control boards have been replaced for a bad pressure switch, or inducer motor, or pressure switch, so don't just assume the board is bad. The control board it probably the toughest part in the system!
Occasionally the gas valve just doesn't open. You might hear it might click, but the valve may still not open.
You do have gas? I have gone on no heat calls and the LP tank was empty, or someone shut off the gas valve to the unit.
Good luck!