Strain is a catch-all for your non-lethal damage. It represence mental trauma and fatigue.
Coercion is the skill in FFG Star Wars Roleplay typically used for intimidation. It's a social skill to represent a battle of wills against an opponent.
Scathing Tirade allows you to make a coercion check against an adversary in short range as an action to deal strain for each uncancelled success generated, plus additional strain equal to the number of uncancelled advantage. Note that strain suffered in this way is not affected by soak.
The improved Scathing Tirade also gives the affected target a setback die as well.
Finally, the Supreme scathing tirade allows you to suffer one point of strain on yourself to do that as a maneuver. Effectively allowing you to perform Scathing Tirade up to 3 times a round at the cost of significant amount of strain to yourself.
When a target's suffered strain exceeds their strain threshold the adversary is "knocked unconscious." this could translate to anything narratively. Usually as a GM I say that the target was so intimidated that it gave up or ran away rather than pass out from the verbal abuse.
A classic example of scathing tirade is the intro scene to Full Metal Jacket. I decided not to link the video because of explicit language that might not be suitable for public boards.