Questions re: skill points and retraining

[Captain Dobie]

I am a little confused about the whole skill point thing. What is the benefit to retraining skills and what do you do with the skill points? It sounds expensive from what I have read. Also was wondering what the little bubbles are around each of the skills? On my skills many of them have 1 bubble on the left, others when I clicked on them went up to higher levels, but I don't know what any of that means. I would assume that the more bubbles the higher their effect, but I could be wrong. Sorry, if this is covered somewhere else... I looked and didn't find any other links to answer this.