Is your global rank your rank out of all players or out of players that are the same belt as you? And is it determined by your win percentage?

it's based on elo rank
i don't know how it works though

I think DrHax (ToribashTakeOVER) made a video about this. Search him up on youtube and search for his video. I would link you it but i'm on my phone.

p.s. i think this belongs in begginer sanctuary

What I took from that video was that if you play good people in a certain mod and win, your elo goes up which means your rank goes up. But what determines how much it goes up by? For example if my elo is like 1600 and I play someone with an elo of 1680 in a specific mod and I win, how much does my elo go up and how much does his go down? Same goes for global ranks, if someone ranked 1 gets beat by a rank 10000, how much does the rank change after that match?

But can anyone explain why is it that even when I lose to someone of a higher belt or rank than me, that my rank gets better?

Here is a detailed explanation of the "elo" ranking system. That should provide you with all the knowledge about it than you will ever need.
http://en.wikipedia.org/wiki/Elo_rating_system