I am not a lawyer and have no form of qualification in any legal sector. If you are a lawyer and identified something that I have said is wrong then please correct me.
A very helpful website
I am a big fan of this website http://choosealicense.com/ which puts licenses in simple terms. As this is for ComputerCraft projects, I would recommend keeping to the simpler licenses (such as MIT). Whichever you choose, I would recommend reading the full license text and not just the summary information.
I don't want a license
By not providing one you implicitly reserve all rights to your code (see http://choosealicense.com/no-license/), this means that your users can not (legally) use your code. Quite often people who don't provide a license want to reserve no rights, in which case you should try the Unlicense.
Adding the license to your code
It is recommended that you post the full license at the top of each file which makes your code. I can understand the reason for this but also realise how much of a nuisance it will be (sometimes the license will be longer than the code it deals with). Instead, I would advise having a link to the license you are using. I would also recommend that you put the license in you forum post (I have a tutorial on making one of those too).
Someone posted code but I couldn't find a license
As said above, not providing a license defaults to all rights reserved. Your best option would be to point them to this thread so that they can choose their own license.
If that takes too long then you may want to try some guesswork, they shared their code so one could presume that they want others to use it. If you want to modify it then it would be polite to not redistribute your modified version. Or you could avoid the legal grey area and write your own program which does the same thing.
Can I do something outside of the license with my code? What about changing the license or having multiple licenses?
A license is an agreement between you and other users. If the code is yours, you are not bound by the license which you have chosen, meaning that you can do anything with your code. In fact, you can have two or more licenses for the same code or project to different people or even change the license. You can even provide two licenses side by side, allowing the user to pick which one the want to use.
As for changing the license, if people have an earlier version of the project they must still use the older license, however if they update then they should use the new license.
Licenses change versions too, some licenses have clauses which allow the user to use a newer version of the same license even though the project was placed under the older version of that license. (I belive GPL does this).
I have different things in my project (such as code with artwork) can the be licensed separately?
Yes, so long as you are clear about what license applies to which parts of the project.
Example, say you have made a mod for MineCraft (perhaps it's a new ComputerCraft peripheral). You have two parts to your project, the code which makes it work and the artwork - the models and textures that players see in-game. Your code can be under one license and your artwork can be under another one (may I suggest creative commons?)
I'm licensing something that's not code
Sometimes a software license can work for something which is not software, in fact, some open source hardware use licenses made for software. Just read the license that you want to use and think to yourself "does this fit my project?"
If it's artwork of some kind then you'll be better of using creative commons, they have their own website to guide you through the licensing process: https://creativecomm...hare-your-work/
Documentation can fit in both categories, and there are some licenses made for documentation.
More information can be found here: http://choosealicens...m/non-software/