Add ability to invoker
It's preferable to have all abilities under a separate child GameObject, or every ability under it's own child GameObject. This wont bog down the root GameObject with lots of components and make for a clearer structure.
Before you add an ability to an invoker, make sure that the root GameObject has an Ability invoker-component attached.
First, select the ability which you want to add to an invoker.
Next, in the scene hierarchy, select the game-object that should be the caster of the current ability, and click one of the buttons under Add to selected gameobject.
When you add an ability it will try to automatically resolve its dependencies (f.eg it's invoker) from its inter-GameObject hierarchy.
See also: Casting and invoking abilities, Directional ability component, Projectile ability component, Raycast ability component, Create new ability