LastChaos Guide: Kinds of Skills
1) Special skills can be purchased from various NPCs depending on the skill you wish to advance in.
2) processing skills are acquired from specialists in the type of material you wish to process.
3) Crafting skills from smiths and alchemists. They can also allow you to craft weapons, armor, potions, and crystals from raw or crafting materials. The higher your abilities in these areas, the better the items you will be able to craft.
Also you can left-click the skill icon and hover your mouse cursor over the selected icon to get more information on a skill. This will bring up the skill information tag, detailing any information on that skill.