Examples: "After being trapped in a building by hostage-taking terrorists" or "When a woman discovers her long lost twin is still alive" or "When a mild-mannered dentist is framed for murder."
The inciting incident is what sets your story in motion. What happens near the beginning of the story and how does that affect the character? Often, you can begin your inciting incident with the words "When" or "After." In the "Die Hard" example above, "After being trapped in a building" is the inciting incident because without that initial action, we'd have no story.
What happens if you leave out the inciting incident? Without it, we might have no context as to why your character is doing what they are doing in your script. For example, instead of just writing "A cop must stop a bad guy" write "When a bad guy plants bombs in a major city, a cop must stop him before the city's annual parade occurs." Otherwise, we don't know or care why a cop must stop a random bad guy - the cop got called to the mission for a reason, after all, and that reason is the inciting incident (a bad guy plants bombs in a major city).
So think about what happens in your Act I so the reader of your logline understands why your character is doing what they're doing the rest of the script. If you're stuck, look at movie trailers (the full trailers, not the teasers) - they're often edited so that a ten-year-old can understand not only what the character must do, but why they're doing it...in other words, the character is responding to the inciting incident.