Finding out technical stuff! Can you tell me what i need to know?

Hello my fellow Steemers

Tonight i took some time to look around Steemit and read in on what it's all about.
In my first post i wrote something about how i got referred to Steemit by a close friend. He didn't tell me much more then 'go check it out'.
Usually i do a quick background check on unfamiliar websites which require subscription, for some reason ( quantum entanglement for sure) i decided to skip this step and subscribed to Steemit. With this little background info, i was really getting curious to see what Steemit is about.
And boy, have i found some interesting stuff while reading. But the more answers i find, the more questions i have.
Cliché...

Les Questiones
So we (can i say 'we'?) are being developed on/by Git, that's the first cool fact because open-source development beats in-company anytime.
Second plus is we are chain-based platform and thus decentralised. Being decentralized is an absolute necessity for any chain- or coin-based business or application to be successful.
Does SteemIt operate on it's own blockchain network or do we ride along on a bigger chain? I'm curious as it would state something about scalability and further development.

So i knew about Steemcoin and just now about eSteem. Are there more Steembased-coins? /

One post also mentioned there have been about 20 hardforks? Does that mean we roll on about 20 chains or where did the splits go?

So many questions, so little time to read about everything.

Which says im done for today, as we say back here in the Netherlands, my eyes are going to be square if i don't get my eyes off the screen.
I will now have to trust upon the community to provide some answers

Started reading the Steemit white paper, but i better get some sleep first.

Have a good night folks , new post tomorrow