The simplest way to build a fire is to use matches. But there are other materials you can use to produce fire.
Create a Fire with Steel Wool
Get the steel wool and set the contacts of a 9V battery on it. Make sure your fingers don’t get burned as red patches appear on the wool. Blow the smoldering patches. Put on some grass or dry leaves until the flames pop up.
Set the wool and flame down. Add extra kindling if needed. Don’t put too much material on it because it will kill the fire. As the flame grows, put some branches and sticks against it.
Make Fire with Leather Cords
Here is another way to build a fire. Get a foot long wood. Loop the rawhide or leather cord below the stick. The leather shoelace will be just fine. Gather some kindling.
Set the stick on the ground with both feet on the ends. Saw the leather back and forth so it slices in the stick. Keep doing this until the stick dries and blackens. It will produce smoke.
Take some kindling as soon as the embers appear. Set the kindling near the sparks. Blow in the sparks. This will ignite the kindling. Add kindling to the flame slowly. Increase the size of the sticks and twigs. Put more wood along the flaming branch. This will ignite the fire.
Making a Fire Using Lens
Collect some kindling. You can use grass, leaves, twigs or dry moss. Make sure the kindling is dry. Get a magnifying glass. Use it to focus the rays of the sun on the kindling. Blow in the kindling until it generates smoke. Add more kindling so the fire gets bigger. Put the bigger branches close to the fire.
Use as fine a steel wool as possible; they are easier to light up. You can also use various types of batteries, but the 9V is the best. Never use wet wood for lighting a fire; it will not work. Make sure the wood is totally dry. If you have matches, keep them dry.
Be careful when putting additional twigs and branches into the fire. Do not get too close you get burned. Never let small children start the fire. Have water nearby so you can put the fire out.
There are other ways to build a fire, but these methods are the simplest. However, you need to be patient. In some cases it will take a while before the kindling is set aflame.