Som stuff really short, if that helps:
You get Experience Points (XP). Its shown in percent (%) in your profile. If it reaches 100 % (100 or 200 XP) than you get another Progression Point (PP).
If you have some PP then you start thinking about training a certain skill. Could be a good idea to train the skill you are currently using a lot (sword skill, mining or similar). You need to go to some NPC that trains your skill (you have to find one..) and click on the book symbol in the NPC menu.
If your skill is not there, only other ones ore even none, then you have to find a different NPC.
If you select your skill (let it be sword skill), the you see different coloured bars there.
The yellow bar is showing the amount of PP you need to train at the NPC before you can start using that skill in praxis.
The blue bar shows how much PP you have in comparision to the yellow bar. If it is longer than the yellow bar, then you have enough PP, if not: You have to gain more XP and PP.
The red bar starts right after the yellow bar and shows how much practice points you still need. You would gain these for the sword skill while actually using a skill, but you only start getting practice points when the whole yellow bar turned green (see below).
First you don't have any green bar, but as soon as you pressed the train button while having selected the skill at a NPC, some part of the yellow bar will turn green. If the whole (former) yellow bar turned green, then your theoretical training is over and you can start using the skill in praxis (using our sword).
Manual to read with this:
http://www.planeshift.it/guide/en/guide-skills.htmlhttp://www.planeshift.it/faq.html -> Colors and GUI
@others:
I actually think that the color graphic has to go directly into the players guide!