General information:
Skills are Abilities which players can learn. Each class has its own unique skill set. In order to learn a skill, players must purchase a Skill Book from a Grocer and double click to learn it. Once learnt, the skill's level can be improved, increasing its effects; with level 10 being the max skill level.

Skills books for swordsman classes (Orange book) and explorer classes (light blue book) can be purchased at Argent's Grocer; skill books for herbalist classes (green book) can be purchased at Shaitan's Grocer and skill books for Hunter Classes (Yellow book) can be purchased at Icicle's Grocer.

Moreover, most skills have a certain requirement in the form of needing to have another skill at a certain level before it can be learnt. As such, it is recommended to carefully distribute skill points and plan ahead.
Skills can be leveled up, taken a look at and used in the skill bar, for which the keyboard Shortcut is Alt + S.

Skill points:
Skill points are used to learn and level up skills and they are obtained by leveling up. One skill point per level after Lv9 and an additional skill point every 5 levels at Lv65 and above means that skill points are limited. Player are hence advised to spend them wisely because not all skills can be leveled up to obtain their full effects. Choose wisely!

Active and Passive skills:
There are two main types of skills in the game, active and passive.
Active skills are those which have to be used in order for their effect to be seen. These can be temporary stat boosts or targeted skills which deal damage or interract with the target in another way. These skills consume Spirit Points (SP) and have a cooldown.
Skills can be used by double-clicking on their icon in the skill bar or by placing them at the Hotbar, where they can be used by pressing the designated F key or by clicking on them.
Passive skills are those which cannot be used, instead they give a permanent effect to the character. This effect is almost always in the form of a permanent stat boost. They do not cost SP nor do they have a cooldown, however some passive skills may require a certain condition in order to give an effect.

Life skills and Fairy skills:
Besides "normal" skills which are located under the Sword button in the skillbar, there are two other icons with their own respective skills.

The Axe icon displays life skills. These are special skills which are required to do certain activites in the world of ToP, such as chop Trees, mine Ores, salvage sunken ships or fish.

These skills function as normal skills do and can be learnt by purchasing blue skill books at a grocer and their level can be improved, however, they require life skill points instead. These can be obtained by doing Story Quests.

The fairy icon displays fairy skills. These are special as they require a Fairy to be active and they consume the fairy's stamina instead of player's SP.

Additionally, they can only be learnt by using special fairy skill books and their level cannot be improved, with the exception of Fairy Possession.