Skill editor question

First section in skill editor, what mean for cost in this section?

Is this the cost required to unlock the ability through coins, or the cost required to use this skill, such as using mp to activate skill?

The cost is the cost to use the skill; like mana costs to cast a spell.

“Costs” are really exactly the same as “Effects”, except that you have to pay them in full (whereas effects can be applied only partially. For example, a healing power with a +10 health effect will heal someone by 5 points if their health is only 5 points below maximum, but a healing power with a +10 health cost will only heal someone if they can actually accept a full 10 more points of health)

Usually your costs will be negative, and will be taking mana or rage from the user of the ability. And usually the effects will also be negative, taking health from the target of the ability. But you can do things differently than that if desired!