Venmo Tip Jar @AndrewDIY
Furnaces are designed with lots of safeties to prevent fatal and tragic accidents. If any of these featured safeties fail the furnace should stop working all together. Unfortunately this can leave you in the cold which is why you're probably watching this video so let's get to it... Behind the cover of your furnace are all the switches, boards and parts that you'll likely need to check.

There is likely a wheel shaped spinning thing (I'm using layman's terms here) That connects to a vacuum switch that engages and tells the furnace that there is adequate ventilation, blowing away the toxic gasses like carbon monoxide. If that does't spin when the furnace is initiated, you may have a ventilation failure. If the fan spins and nothing happens beyond that you may have a failed ignitor. If the fan kicks on, the glow plug fires up and it ignites but only goes for a short time you may have a failed flame sensor. You can turn the furnace off and remove it, sand off all the corrosion and reinstall it, this may be the solution you need.

If that doesn't work there's usually a window on the lower door of your furnace, through the window there is an LED, a little light. That light will often blink an error code, a number of flashes which can tell you the problem. These error codes vary from manufacturer to manufacturer so if you can't find the service manual look it up online.

Hopefully something in this video was helpful. If it was, you can help me out by liking this video. Please let me know in the comments below if you have anything to add. There's lots of other videos on furnace repair so hopefully you can find a solution and get back to being warm. In the meantime remember to layer clothes and the old adage that "Cotton Kills". Cotton is not a good insulator at all. Good luck.