The Skills Window (K) displays Active skills when opened. Other tabs include Passive, Craft, Emotes, Actions, and Skill Chains. As new skills are learned, they are added to the list.
Hovering over an skill icon will display the name, description, target, cast time, cooldown, and trigger rate, as well as any requirements such as a melee weapon. The lower left corner can be checked to display only the highest level of each learned skill.
Passive skills are automatically used once learned. Some are auto-learned but most must be purchased from a Skill trainer.
Crafting skills will display proficiency levels in any learned craft, Essencetapping or Aethertapping. Morph Substances does not increase in level.
The Emotes are listed under that tab, and the Actions under its tab. Clicking on the Chains arrow opens the Skill Information Window.