Okay, this has probably been asked before, but how do I add music to my map? I've tried everything, but can't find a single tutorial anywhere. I can't even figure out how to play existing tracks, can somebody try to answer as soon as possible?

Use an ambient_generic and mark the "play everywhere" flag. For music you'll want to reference the name in "level_sounds_music_portal.txt" (i.e., use "Portal.song1" rather than "music/portal_subject_name_here.mp3"). This way the game will recognize the sound as music, and the music volume knob will work correctly.

EDIT: Exactly what Mevious said...

Mevious wrote:
[...]and the music volume knob will work correctly.

Hey, I never thought about that. Better check if mine are set up correctly! Thanks for the tip.

I'm sorry, some of that is kinda vague. I set it up like you said but it still doesn't play, you have to explain better I think.

Oh it's actually sound...not sounds.

My mistake, see if it works now.

No, I understand that, but somethings being left out, if I could have a step by step walkthrough of it that would be great.

WOOHOO!!! 100th POST!!!

I find that ambient_generics have a lot of unexpected behaviors and bugs. For example, sometimes I have trouble with "Start Silent" unselected. Go here and you'll see loads of documented bugs http://developer.valvesoftware.com/wiki/Ambient_generic. Other possible problems are that it can't find your sound file or your sound is the wrong bitrate. You'll need to debug it yourself. Take a look at your console for errors after the sound is triggered. Set ent_messages_show 1 to see entity IO in the map and make sure the ambient_generic is triggered in the first place. You can also use VMEX to decompile an official map and copy exactly what they do.