the title is pretty self-explanetory
in radiant, open the entity window (N key) and scroll down to the bottom. Select 'worldspawn'. In the 'key' field, type 'music'. In the 'value' field, type the path to the music file. If the music came with the game, you can find the path in the assets0.pk3 file in your base folder. Use forward slashes (/) only, not backslashes (\) in the file name. If your music is custom, make a folder in your base folder named 'music', and in that folder make a folder with your map name as the title. In that folder, put your music file (.mp3 and .wav only). Then type the path in radiant (see above) and it should be something like this:
Music from the game: music/mapname/musicfilename.mp3
Custom: music/yourmapname/musicfilename.mp3 or .wav
hope this helps ~Dev
Let me explain it in a simple way:
1)Open your map (If already open then reopen it)
2)Before you do this make sure you have just loaded your map and press n
3)In the colum labled "key" type: music
4)In the colum labled "value" type: music/yourmusic.mp3
where it says yourmusic.mp3 replace it with the name of your mp3 file
5)Now save your map
6)creat a new folder and call it music
7)put music into base
8)drag your mp3 file into the folder you just put into base "music"
Now bsp your map and it should work.
Isnt that what Devmapall said?
thanks guys it helped