Try to make a simple mod but stuck in gui

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I'm making a simple mod for the people who can't afford mic in my group. 

Basically the mod gives you options which sound file to play and plays it via playSound3D during gameplay.

I tried to figure it out by myself but I can't get GUI to work. I followed all those youtube videos or guides step by step and it didn't work. 

 

Can someone provide me a simple working gui template so I can edit or add on it. Or just example? 

 

I was trying to make the mod like this:

press certain key - menu gui pops up - choose category (Report, Status, Request) -  player chooses which audio files to play - audio plays via playsound3D. (I believe Say3D is not suited for MP) 

 

Thank you.