Gas furnaces are by nature dangerous.
To make them work safely they are designed with a variety of clever systems that prevent accidents. Tampering with the safety systems is extremely dangerous.
The pilot light in a furnace is the small flame that burns all the time. When you turn up the thermostat, the gas valve opens, allowing gas to enter the combustion chamber where it is ignited by the pilot.
Even the small amount of gas going to the pilot would build up to dangerous levels if the gas flow to the pilot didn’t stop if the flame went out.
However, the gas flow is stopped because of the thermocouple. The thermocouple has its tip in the pilot flame and is connected to the gas valve by a pair of wires. As long as it stays hot, it tells the gas valve to keep sending gas to the pilot. If the pilot goes out for any reason, the thermocouple quickly cools off and sends a signal to the gas valve to shut off all gas flow.
The gas valve, located where the gas supply line comes into the furnace, will have a red override button and an adjustment knob that can be set to “Off”, “Pilot”, and “on”.
The off position would be used in the summer to shut off all gas to the furnace, even the pilot.
When you turn the knob to “Pilot” you will be able to push down the red override button. As long as you hold it down, gas will flow to the pilot. This allows you to light the pilot. You need to hold the override down for a minute or so to give to give the thermocouple time to warm up. Once that happens, you can release the override and the pilot will stay lit.
If you have a newer furnace it may come with an electronic igniter. In that case you hold down the override and electric sparks ignite the gas. On older furnaces you have to get a flame into the combustion chamber and actually light the pilot. This can be more of a challenge than you might expect
Especially on windy days, there will be air moving inside the combustion chamber. It will be strong enough to blow out matches; which is really frustrating. However, this draft will be strongest just inside the door and the pilot will be farther in. So, the trick is to insert the flame quickly.
Some furnaces come with a long match holder that will allow you to quickly reach the pilot at the back of the combustion chamber.
Instead of marches, one of the “campfire” style butane lighters may be long enough to reach the pilot and would not be blown out by the draft.
I also had good luck with fireplace matches. These matches are about a foot long, produce a large flame and would reach the pilot without blowing out.
The trick is, you usually need one hand to hold down the override button, one hand to hold open the spring loaded door to the combustion chamber and still another hand to actually insert the match/lighter into the furnace. The difficulty is compounded if your eyesight isn’t so good because it is dark inside and hard to see what you are doing.