mining theory – basics of cryptocurrency

I recently became interested in cryptocurrency and its mining process but there are a few things I don’t understand very well and I am still trying to learn the basics more before getting into trading and mining. I am totally new to this and still looking around to just understand it first.

  1. i read that currency is mined by solving cryptographic equations. what are these equations basically and what are they used for and apart from you getting a reward for solving them i.e. cryptocurrency
  2. apart from you who or what else benefits from the solution of such equations like what is the impact of it
  3. what made these equations i.e. their origin
  4. is the 21million limit on bitcoin fixed or can it be changed. on a website I read that this limit has been determined from extrapolating its existing functions and parameters.

Apart from this any helpful information or websites to learn from would be greatly appreciated because I realize that this is very complex and it will take me a while to familiarize myself with it. Thank you