Just to reiterate, if it's an event you'll use multiple times, then stick it under Common Events and call on it whenever you need it. If it's something simpler, like a cutscene or whatever that you only want to happen ONCE, then simply place "Change Switch: [Desired switch]=ON" at the end of your event. Then, create a new page with your event and make it nothing. Make it so that the switch you turned on in the first page is required to be on for the second page to be activated by checking the first box on the second page and selecting your desired switch into the label. I hope that helps!