At the site you've chosen, clear the ground of any thing that could catch fire from a spark popping out of the fire.
Three feet all around the ring is a decent guide.
If you are not using a pre-existing fire ring, consider how you will get the area you use back to the state it was in when you found it when you leave the site.
Practice a leave no trace philosophy and minimally impact the land.
Whatever you do to enclose the fire base whether it is digging a small hole, building a fire ring with rocks, or both, do it in a way you can put things back the way you found them.
Whatever you choose, be sure there is adequate air flow to provide the air the fire needs or at least give your self an option to easily make a modification should you need.
On to the building, which is exactly what you are doing - building a fire.
With a good foundation you'll stay warm all night and just have to make a few passes over the sparker.
Think about how the fire will spread once there is a flame.
The concept is that you get a flame into a large fist-sized bunch of tinder that starts generating heat.
The hotter this becomes, the thicker the pieces the flames will spread to.
Generally there are three types of structure styles you can use.
These three will start with a flame in the center and the fire will grow until the whole thing is burning.
Some are better for cooking than for sitting around, but you can experiment and find what works best for your needs.
I will generally use a log-cabin style frame where two large pieces of wood are set parallel to each other on opposite sides of what you want to be the center of the fire.
Space them far enough apart where they will be able to support two more parallel logs that complete a square-ish shape.
You have just framed your fire.
Next, within the box, place some medium sized pieces.
You want density, but not overly dense where air will not flow.
Keep space in the center for a large-fist or maybe even two fists worth of the small pieces.
Build your tinder bundle next.
Pull out three of the cotton balls and spread the fibers of each as much as possible while keeping it mostly in tact.
Take some small sticks and twigs and make a nice little bunch of kindling to add to the center of your fire structure.
Stretch out one more cotton ball and place it on the bundle.
You will shave the magnesium bar into this cotton ball shortly.
Place this ball of stuff in your fire structure with the last cotton ball you added facing up.
Stand back and have a look at what you've built.
Is it safe to make a fire here? Will there be enough air flow? Do you have more fuel close by to easily add to the flames as needed? Can you see the small flames being able to burn the small pieces and move on to the bigger pieces as the fire gets hotter? Is it safe to make a fire here? Yes to all these? Continue.
OK.
Take out that magnesium bar and start scraping/shaving the metal onto that last cotton ball you added.
The flakes of metal will be light so if there is a breeze, you may need to get pretty close to where you want the shavings to fall.
Build up a decent amount of shavings on the cotton ball.
You'll use the spark strip on the bar to shower this area with sparks so have enough magnesium flakes there to catch a spark or two.
This has been part three in a four part series.
Keep a look out for part 4!