What does "missionPlayDialogue" do?

Im making an event and i want a bomber formation to spawn but i also want a giant notification that i can type out to appear on the top. some thing like how gaijin does it in ground battles to say “Capture the enemy point” Ive no idea how to do that, i was thinking the “missionPlayDialogue” would help but i have to create a dialogue and i have no idea where to do that

Not possible. You need a additional text file to play dialog just like Gaijin does it. You can however use “playhint” action to create a dialog line on-screen. However it’ll be at the bottom middle of the screen.