You need to reference an effect. The simplest way is to use an existing one. Open effects\base.effects.darkest file and look for a stress heal. Once you find it, add this to the skill code:
.effect “name_of_your_effect”
For example:
combat_skill: .id “omniscient_light” .level 1 .heal 5 7 .launch 43 .target @4321 .effect “Heal Stress 1”
This skill will heal single ally for 5-7 health and 4 stress. You can have multiple effects per skill.