Minecraft not only has a very creative community, but also a very active modding community that adds things like new monsters, new items, texture packs, minimaps, and other tidbits that improve on the game for the end user.
On Accelerated Ideas, a tutorial for people with some programming experience has been posted for a while, but I just now came across it. The tutorial details what programs you will need to alter the source code of Minecraft, along with links and resources for the aspiring modder.
The code of Minecraft itself is very well-structured and works on a very straightforward engine, meaning it’s not difficult to edit or mod at all once you find out how the program actually works behind the scenes.
The guide covers everything you need to know from decompiling Minecraft’s code, recompiling, and how to make some simple edits. It only details the actual starting of the process since a guide on programming just about anything can fill a small book several times over.
The modding community of Minecraft is very active on the various unofficial sites and is perfectly acceptable and accepting of newbies. The trick with any kind of modding is to start small, changing graphics and textures to see what files work and what don’t. Changing non-game-mechanic details are among the most common forms of modding. After that, you can upgrade yourself to altering the speed of a zombie or the blast radius of a creeper, and perhaps even the flammability of certain objects. Minimaps, creepers that physically jump at you in an inescapable kamikaze attack, and ziplines are just some of the things the modding community of Minecraft has accomplished. Try your hand at it if you have the time.
Image is from the Prismatic Minecraft mod by radicalTERRA on DeviantArt.