Read the technical documentation and read the source code of Bitcoin Core.
A good start.
If you want to learn it properly, implement your own coin and network - from scratch.
No, I just want to understand everything about Bitcoin, blockchains and whatnot. I want to also have the ability to judge, technically, if a project is viable or not.
Then you must have a lot of research on that, there's a lot of discussion here regarding your concerned you must read and learn, try to go on Development & Technical Discussion here's the link.