This script allows you to create "skill links" which are basically a way to connect skill effects together.
Skill links are purely a development concept: they are created to allow you to specify multiple behavior that should occur when a single skill is used. In particular, it allows a single skill to execute damage formulas and effects under different scopes.
For example, suppose you wanted to create a skill that damages the enemies, but also heals all allies as a secondary effect. By default, there is no easy way to accomplish this without resorting to common events or complex formulas, and even that may have its own limitations.
However, there are few things that you CAN do.
It is easy to create a skill that will damage all enemies
It is also easy to create a skill that will heal all allies.
This script introduces the link between the two skills: you simply specify the healing skill as a "linked skill" to the damaging skill, and now whenever you execute the damaging skill, the healing skill will automatically run as well.