I always do it in these two ways:>"Low fantasy style"
To understand "magic" you must first understand what fuels it, some people call it "chi" others call it "mana" whatever you choose to call it, this "energy" is everywhere and flows through everything, living beings generate this energy continuosly and that's why some people call it by my favorite word wich is the "soul".
Either way, fires are know to also generate this energy, does the fire have a soul? Is it alive? I like to think so.
Now that you understand what fuels it, comes the hard part. Understanding how to manipulate this... thing.
For the ones who can do it it's quite a simple endeavor, it's like folks who can move their ears, it's hard for them to even explain how they do it, they just can.
Since you willing to listen I can tell you that whatever is the thing that let us mold this energy is directly linked to our toughts, so when I control the flames I can sense it passing through me and connecting me and the fire allowing me to slowly affect it and mold it as I want it to be.
And it surely affects the world around us, this was just a forest centuries ago, now it's the infamous "dark forest" or "shadow forest" or whatever the villagers call it, for the toughts of thousands molded the energy concentrated here into these darker woods and dense leaves.
These effects are vast, some people can project feelings and their will on others, some can help the healing process of the body, some can manipulate fire, water and the air, and most likely, some can use it without even noticing.
For years, this energy will affect their bodies to reach a desired result, creating wonders like the legendary Herkiles who some said had muscles so strong he could strangle a lion with one arm.
That big man of a champion on the arena yesterday who had a skin so tough that arrows couldn't pierce it and swords barely cut it, how do you think his skin turned out like that?
Magic, little one... Magic.