Lore question about magic, ninja techniques, and other.

First I should say that I'm not really sure what I expect potential answers to be like. The questions I'm going to ask are all about the extreme fundamentals of magic, which is something that Riot hasn't really gone into that much (I think). I mean, some writers don't go into this stuff at all, because it's magic. Yeah, onto the questions. I guess I'm trying to figure out… what is mana? When someone, let's say Lux, casts a spell, what exactly is happening? What's fueling the spell? What is Lux giving up in order to obtain the desired effect? According to the game, she's giving up mana and time (cooldowns), but that's according to the game. In the lore, again, what is mana? Why can't a mage just fire off spells infinitely? And then there are people like Riven and Yasuo. They're not exactly using magic, they're using martial arts techniques. So when Riven throws out a blast of Ki energy, where does that come from? Why does she have to wait before she can use it again? And then there's all of this but with energy instead of mana, like, what makes ninjas different? And then I know that there are different sources of magic. I'm pretty sure that Lux, a Vastaya like Ahri, and a Yordle like Lulu all draw magic from different places. And then, where do godlike beings like Bard and Sol get their magic? Where does it come from? What are the consequences of using magic? Re-read the intro and then we're good.