/splay -cwmpq [filename | stop | pause | resume | seek | skip] [pos]
You can try "/help /splay" in mIRC to get more info.
Assuming you're using Glitch.com as a script editor, and running the scripts locally on your machine, you just need to know the filepath and filename of the sound you want to play.
Let's assume you want to play Laugh.mp3, so you just need to know the filepath. Let's say you copied the sound file into your mIRC folder and placed it in the folder named "sounds", so your filepath would be
$mircdir $+ sounds\Laugh.mp3
Then you just use /splay...
/splay $mircdir $+ sounds\Laugh.mp3
I've never heard of Glitch.com before, but assuming it's just an editor for mIRC scripts, I thought I'd bring up MSL Dev, the mIRC Script Language Developer.[Click here to get it for Windows or Linux]
It's a very robust and colorful editor, with it's only shortcoming being that it hasn't been updated since 2013, but even then, I still use it today.