This example is for playing or not playing looped music when asked by a text message but you can change it to any event you want .

First off is to put a string in your pstr.txt like the one below

string 84
Do you want to turn on the radio ?
Press Y or N
~yu43=1~nu43=2
sdone

The text message is number 84 and the Ureg that triggers the event is number 43 , so if you press key Y ureg 43 is set to value 1 and if you press key N the value is set to 2 , now you need an animation that will check for Ureg 43 and meet a condition when the ureg is at the values set , something like the one below .

EG
Frame 0 Branch if close to frame 2
Frame 1 Unconditional branch to frame 0
Frame 2 Display text message 84
Frame 3 Skip if Ureg 34=1
Frame 4 Remove this animation
Frame 5 Play sound ( sound number )
Frame 6 No operation just a delay the length of the sound file
Frame 7 Unconditional branch to frame 5

You would put the animation near to a radio and mark it as invisible , then when the player approaches the message will appear asking you for an input , if you press Y the music will play , if you press N it will not .