How do you put Portal 2 music into a map or have GLaDOS, Wheatley, or the announcer say something?

Music is an ambient_generic with the "Play everywhere" flag checked. I think you have to place an instance with a generic_actor and use logic_choreographed_scenes on it to create GlaDOS/Announcer lines. Someone else can probably explain this better than me.

Yeah, could someone explain that in more detail? Like what do you need for the outputs and settings?

What makes the characters speak are GENERIC_ACTORS which then activate 'scenes' which control what voice is played PLUS what animations will happen when they are speaking. GLaDOS wasn't faceposed however Wheatley was, so in the scene file for Wheatley there will be 'gestures' as well as the dialogue played with them. You can play a scene by using a logic_choreographed_scene and use the 'Start' input.

Creating a custom scene is impossible without completely rebuilding scenes.image using the Portal 2 faceposer, however you can find a list of (or use) Valve's scenes inside pak01_dir.vpk root/scenes/npc/actorname

Music is played through an ambient_generic with the 'playeverywhere' flag checked and they fade out using the 'StopSound' output. Valve only used scripting for playing music that happens when you are in funnels on Paint, etc.