How Should I proceed.
To do what, exactly ? What is your goal ? This is the most important question right there.
I have gone through the book "Mastering Bitcoin" and I am not able to completely grasp it. I just need a break from reading and need to do something practical.
Is "
https://github.com/bitcoin/bitcoin/" is the original copy?
How should I read the source code?
Do I need to install some specific program /compilers for it
The Bitcoin Core source code is hard to read. As you're asking if you need some kind of compilers or anything to build it, I assume you are not a skilled c++ software developer (which is not wrong!), but it will be even harder for you to read. You should not try this way.
If you want to understand how bitcoin works, installed the Bitcoin Core (wallet) client already compiled (on
https://bitcoin.org/), and try it using the
Testnet. After you got a grasp on how the wallet works, I would advise you to take a look to the RPC commands (accessible using bitcoin-cli). It will allow you to use the wallet, but using bitcoin core features even closer to the protocol. If you are a software developer, you can try to build a simple explorer, using those RPC commands, or even a blockchain parser. It is a nice way to understand Bitcoin even deeper, and not much an hard task. Once you've done all that, you'll be mostly ready to understand the Bitcoin Core's C++ code! :-)