I am looking to understand the Bitcoin C++ source code on GitHub. The Python one is simpler, but even that is too complicated for a beginner. Could someone guide me to some good resources on the actual implementation and its details? The actual C++ techniques used seem to be quite complicated.
I am not aware of an extensively commented version of the Bitcoin sourcecode, but you could check out the Bitcoin Developer Reference and you can read online the book Mastering Bitcoin by Andreas M. Antonopoulos, which covers Bitcoin's technical aspects extensively. There is also Princeton's Free Online Bitcoin course, which goes into details on some technical aspects, which might in turn help you understand the sourcecode better.
Besides that, try searching Bitcoin.SE for specific questions, there are a few here that have been asked about already, if you can't find something, feel free to ask a new question here.
My new book "A Dissection of Bitcoin" examines the original Bitcoin source code written by Satoshi.
As for now, it is the first and only book available that helps you read the Bitcoin source code.
Aside from what @Murch♦ mentioned above (especially the developer reference), a good source for this is the Doxygen documentation. You can generate it locally or it seems to be published here:
Unfortunately the documentation itself is pretty sparse, but the things that Doxygen adds (especially call graphs and inheritance graphs) add a lot more than what you would get just by browsing the source in an editor.
The Bitcoin codebase is a very large today, with roughly 370,000 lines of code in the 0.17.0 release.
There is a Github project that help developers read open source projects. Check out the entry on Bitcoin:
It contains an overview of the Bitcoin codebase as well as some tips to get you started.
You might benefit from understanding key concepts in bitcoin before diving into the core source code. The following link teaches the technical basics of how Bitcoin works by walking you through writing a simple python script to create transactions from scratch:
Also on the site are other posts on how Bitcoin mining works and how to write a python script to mine Bitcoins (for science and understanding, PROFITABLE cpu/gpu mining days are long gone)
You might benefit from some fundamentals of what the Bitcoin blockchain actualy is. James D'Angelo is awesome at explaining concepts to everyone including beginners and more advanced users, without being boring or confusing. Watch the following video and check out his channel for more info. https://www.youtube.com/watch?v=gUwXCt1qkBU
Mastering Bitcoin by Andreas Antonopoulos is definitely a good start. It's available for free.