I don't understand what you mean. To add sounds to the server you would have to upload them via FTP into the "sound" directory located in the server's Garry's Mod root directory.
If you uploaded a soundfile into "sound/my_sounds/hello.mp3" you would this to play it:
ulx playsound "my_sounds/hello.mp3"
Keep in mind that you would have to make sure that people download them, either using
resource.AddFile in a Lua script, or using ULX's forced downloads:
/index.php/topic,3072.0.htmlIn ULX, there isn't any "addsound" command and probably won't ever be unless Garry adds some support for downloading soundfiles similar to
PlayURL