The simplest answer is a Switch or a Self-Switch depending on how you access it. That is, a car can change where it goes just by the Self-Switch driving it and by a Switch sitting in the middle of the road.
You can also right-click on the map maker and pull up a treasure chest, an example of an event that works once (You can even remove the item and change the included textbox).
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Basic Level: Say you want to have a Rock blocking your path until you punch it.
From scratch, make a New Page on your Rock Event so you have two pages. Make the left page have an image of a rock and have the empty right page require a condition of a Switch being on (page priorities are usually right to left). Now, first page, you can have the switch turn on, and if the event requires an Action Button, what happens is that you punch the rock, it runs that page which turns on the switch, and with the switch on, that other page goes on.
aka:
Page 0-
.Text: "I am Rock!"
Switch 1 ON
Page 1-(Switch 1 == ON)
Text: "I shall Rock your World!"
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Basic Level 2: Or perhaps you have the rock introduce himself and have normal text later.
From scratch, you only need one page. Give the event a face of a rock, then use a Conditional Branch of a switch being OFF (in event page, not the corner). And in that page, have a bit of text and turn the switch on. That way, you touch it the first time and it runs, but the second time and with the switch being on, that portion in the branch doesn't run.
aka:
Page 0-
Conditional Branch: IF Switch 1 == OFF
.Text: "I am Rock!"
.Switch 1 ON
END
Text: "I shall Rock your World!"