Let's equate 'magic' in PS to a few things in modern times.
A: Gravity. There is no doubt that gravity exists, and people use tools designed to utilize gravity with the push of a button. However, there is not one single person on this planet who actually knows
what gravity is. There are guesses and theories, and many things that say "gravity does this", but nothing that says for certain "gravity IS this". In modern times, gravity is our magic. People use it to make tools, but no one can make gravity.
B: Computer programs. This one is a little closer to how magic works in PS with your characters. Think of Glyphs as an installation and program disc (needs the original disc in the machine while running). Without a computer to install to and run the program, or without the original disc, it does nothing. The Races act as the 'computers' in this case, activating the program and running it. Note here that your characters are like old computers with hardwired hardware, and you would exist as ONLY that computer. You can 'upgrade' them to a certain point through software upgrades (training), but only to that certain point. Once you are to that point, your computer is maxed, that is it. No hardware upgrades (unless you want to try to 'power down and unplug' ((kill)) your character and have a god try to install new hardware

). You may also not image the disc to your HD, as no matter how much you upgrade your computer/character, it will not have enough 'memory' to hold the image. The disc is always needed.
Once you have the glyph/disc/program installed, it does what it is intended to do, no more, no less. The program disc is unhackable/unchangeable. Flame Spire is hardcoded to surround you with flames. It will not surround anything else with flames. Arrow is hardcoded to fly from you to a living enemy. It can not be used to break down doors.
As just a character/computer, you do not have the ability to produce the Glyph/discs. You are not designed to do so. You need to be something with far more power, such as a production factory (aka, a god) with the tools and ability to create the discs.
You may not cast the Ubersuperultradeath unless you have the factory made Ubersuperultradeath disc and your software has been upgraded to that disc's level.
As to understanding what magic is and why it does what it does, go back to example A: Gravity. Why does magic do magic? Because it is magic. Why does gravity affect things the way it does? Because it is gravity.