I think link 2 is explained very well!
This older post may also be helpful:
http://forum.micdoodle8.com/index.php?threads/how-to-code-a-new-planet.1962/
What nobody can do is teach you how to code for Minecraft - or specifically, teach you how to make a good-looking worldgen or structure generators, or how to make new mobs for your new planet. You will need to do that for yourself, and then fit it into the planet framework that's been covered in the tutorials.
Depending on what your existing skills are, those things are pretty hard. I know, because I've actually coded a new planet for Galacticraft (a long time ago before I became involved with the mod), it took me 2 weeks and even then I only had the basic worldgen done and it didn't have any new mobs. It was OK for the server I played on but not good enough for public release. Minecraft worldgen is a fairly specialist skillset, the natural looking world gen in vanilla is actually one of the best features in the game. You could start by looking at that, figuring out how it works, and coding something similar. How about a snow and ice planet, or a water world?