creating a fork of bitcoin, how to modify core to create my own network I'd like to make a fork of Bitcoin, since it's the new trend ;)

The first thing I did was to create a docker image of ubuntu with all the dependencies, then I wanted to run the core software- but the first thing it did after I built it and booted it up was start trying to connect itself to the real-world bitcoin network- not what I want!

What I'd like to do is define my own network, that I can just run on some machines that are under my own personal control- pass around coins- all the typical stuff- check out the wallet- really basic

but I'm at a loss for how to do that. 

I've been told that I need to modify chainparams.cpp, is it so? If yes, then what do I need to do to it? 

Is that the only thing I need to change? if there are other things what are they?
Regtest should really suffice for your basic testing. If you really want to modify chainparams, you would first start with the DNS seed data in the file; these are hard coded.