As previously stated, skill trainer NPC's can be found in many towns. They offer skills exclusive to your current primary and secondary professions that can usually be attained through side quest rewards in the previously explorable areas. They will train you in a skill at the price of one skill point and some gold per skill. some quests actually reward a skill point as a reward.
There are elite skills for each profession that can only be attained by capturing them from a dead boss monster later in the game. This ability requires a "signet of capture" skill, which you must also purchase from a trainer at the cost of one skill point per signet. This skill can be purchased over and over again starting at Quarrel Falls.
Be wary of using too many skill points training in regular skills for you will regret wasting valueable skill points you will need later and can only acquire through xp at 20k xp per skill point once you hit level 20.
Skill points have nothing to do with increasing the strength of the skills you already possess. That is exclusive to attribute points.
Completing regular quests for skills and skill point rewards are the impetus for playing the game.
Hope this helps.
