I'll try my best to explain it...

So i've decided to add pickup notes to my wad, they go in your inventory bar and when you use them It'll start the Use state in decorate which is Acs_execute (It's just a hud message script that displays a picture and after a duration of time it fades out)...

You can keep these notes if you'd like (cause some of them have useful information like the example below) or take em out your inventory for space. I would just like to know how i could fade in the note and let the player cancel the note whenever the player is done reading. Like how The city of the damned: Apocalypse did... (By the gods that wad was amazing... couldn't stop playing once i started...)

Anyway all help is appreciated and thanks in advance!

You could simply check the scripts in TCoTD2

But one thing you definitely need to look at is the HudMessage article on the ZDoom wiki. That will help a lot.