The Skill menu can be opened (alt + s).
You have several types of skills and they are divided into the following categories: Basic, Active, Passive, Clan and Item Mall skills.

Basic Skills
Basic skills are mostly automatically learned and contain skills which are daily used suchs as the Pick Up, PartyTrading, Vending, Duel, Quick Switch functions are in this category.
Also emoticons are listed in this category, these skills are just for fun and can be used to express your feelings.
Not all of the emoticons skills are automatically learned, some of them can be bought later on from [Mysterious Girl] Kitty in City of Junon Polis or from [Little Street Vendor] Mile in Breezy Hills.

Active Skills
Active skills are used by players and monsters. These skills can cast positive or negative conditions or open the crafting windows for Artisans.
Postive conditions are called buffs, each class has it’s own buff and the support class Cleric has the majority of all buffs.
Negative conditions are called debuffs or spells, they weaken the opponent.
Each class has it’s own active skills.

Passive Skills
Passive skills can increase or decrease a player ability.
Each class has it’s own passive skills.

Active and Passive skills for level 1 ~ 199 can be bought from [Mayor] Darren [Mayor] Darren in City of Junon Polis and skills for level 200 ~ 275 [Job Master] Jason [Job Master] Jason also found in City of Junon Polis or in Underground Prison.

Clan Skills
Clan skills are used to preform clan actions suchs as Clan Recall, Clan Assist. These skills can be preformed by the Master and Deputy Masters of the clan.
These skills can be bought from [Clan Manager] Ashland in City of Junon Polis.

Item Mall Skills
Item Mall skills can be bought from the Item Mall, the most famous Item Mall skills are the Harvester and the  Collector

Skill Points
The skill points players earn while leveling can be used to level the skill levels. You can level a skill by clicking on the + icon that is located in the lower right corner of the skill icon.