There is a ton of fairly good information on the internet, including some U-Tube presentations. I have a fairly basic opinion on the matter: find something that works and use it till it bores you. Then (and only then) vary your methods and materials.
I use cotton gun-cleaning bore wipes or cotton T-Shirt. I find a flat tin, like an altoids tin, punch a hole (not holes) in the lid, put the wipes into the tin and place in coals of a fire. When smoke comes out of the hole, pyrolization (the reaction you want) is happening. When the smoke stops, flip the tin over in the coals. More smoke, wait till it stops. Remove from coals and leave alone till it cools. Put the charred cloth into another altoids tin (or other handy watertight container) and you are ready to play.
Pyrolization is a process where you lower the ignition point of some material by exposure to heat with limited oxygen- like making charcoal. Accordingly, I often make "charcloth" with natural tinder- including thin wood-chips. But these require more study for proper preperation so save them for last.
As far as storage is concerned, charcloth must be kept dry, so I have a screw-top container that can be submerged without leaking, into which I place my char-cloth. I am still using some made two years ago.
Properly charred cloth does not burn- it takes a spark and begins to glow. That is the ember you are looking for and it is that tiny ember which will glow when you blow on it and get hotter. It is this that enables fire when placed among very dry tinder that you coach to ignition by blowing.
You do not "throw" sparks into charcloth like with a firesteel. Instead, you catch sparks. Why this distinction? Because I hold the flint in one hand with the charcloth on top of it and very near the striking edge. When I bring the steel into contact with the flint, a spark dances off the top of the flint and is caught by the charcloth. Usually, two to three strikes produces the ember I want.
The ember is durable and will grow while you set the steel down and transfer the flint to your other hand, and continue to grow while you place it into the tinder. On occasion, I merely place the glowing charcloth back into the container with the rest of the charcloth and let it grow while I ready the tinder. (once you do this all anxiety fades because you realize there is plenty of time).
Charcloth that has been over-burned during its creation will crumble like ash. If properly prepared you can pick it up like blackened cloth. I have used cotton Denim and cotton towels as well as cleaning patches, but then you have to cut little square (patches) and place them into the tin to char. I do 20 at a time in one process.
-carl