Regarding GitHub and development environment setup, different people will preach different solutions.
As SubJunk said, you don't need to do any of this to participate on GitHub and create issues or make comments. If you do with to have the ability to "dig in a bit deeper", you will need to set up some kind of development environment in addition. The bare minimum you need is:
- Git installation
- Java JDK (as opposed to the "regular" JRE) installation
- A reasonably capable text editor
In addition to this, most people use an IDE. The IDE fills the role of the text editor, but does much, much more. I'm as helpless with Java without my IDE as I am fixing and engine without my tools. Yes, it is possible to do without it, but it simply doesn't make any sense.
If you want a free and open source IDE for Java, there aren't that many options. I use Eclipse, and in my view it is miles ahead of any other IDE I've used also in other languages before. It can really do amazing things for Java because it is so well integrated with Java (and it is actually written in Java). You can work with other languages in Eclipse as well, and I've tried to use it both for JavaScript and C++, but to be honest, I didn't find that very satisfactory. But, for Java, it's simply "the king" in my opinion. Others will have other opinions though.
Eclipse can be a little bit bitchy to set up, because you have to install some extensions/plugins and know how to configure it to get it set up properly. Some people seem to give up on Eclipse before they get this right, and these people will usually say that "it's crap". That said, no software is "perfect", and the same goes for Eclipse - I've had some annoyances with the latest version. On my "development computer" I have an older version (Eclipse Luna) that I consider to be working pretty much "perfectly" though.
If you want to give Eclipse a try and need some instructions to get going, just ask and I'll do my best to explain.
In addition, you need to be able to do the basic things with Git. Git is one of those things that are brilliant and a complete mess at the same time. Git can be inconsistent, confusing and sometimes a real pain to deal with, but when you get it to do what you want, it's simply a brilliant tools that I don't quite understand why some choose to live without. For Windows, I recommend installing TortoiseGit though.
Git itself is command-line only. You have to type commands, and the feedback you get is in one of those "terminal"/"dos" windows - not always the most elegant or user-friendly way to work. TortoiseGit is one of several "GUI tools" that works on top of Git. All TortoiseGit does is to visually guide you by letting you look at "the Git content" through graphical tools and lets you tell Git what to do through menus instead of having to remember commands and syntax. It still use Git to do the actual work, it simply generates "command lines" that it passes on to Git, so by working this way you're free to use the GUI and the command line in any combinations you want. In the beginning I did almost everything via TortoiseGit's GUI, but as I've gotten more used to it, I now do some things from the command line (because I find it quicker or easier) - but I still use the GUI for many things where I simply consider it very superior to the "bare Git".
Expect to be frustrated by Git though, read some tutorials to get the basic idea of what it does. Git is very complex and there are loads and loads of things that I don't know how works to this day. But, don't let that scare you, since you don't need most of this. The "normal" use most of us need is actually quite simple and straight forward, the problem is that the documentation doesn't really differentiate between "what you need to know" and the complex stuff. So, I recommend trying to get an overview first, so that you can orient yourself enough to know what you're interested in doing, and then figure out how to do just what you need. I personally think TortoiseGit goes a long way to "cushion the impact" when first meeting Git.
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