For every slush, you need an UNOPENED bottle or can of soda.
Shake it up. Shake it hard. You want a LOT of pressure to be built up in that can.
Toss it into the freezer for at least four hours. A half hour before you want to eat your slush, put a cup or bowl into the freezer, too.
Pour it into your chilled bowl. A black bowl was not a good choice for photographs!
Your soda will slush up when it hits the chilled bowl! If it doesn't, toss in an ice cube. That will be the bit of cold it needs to slush.
FYI - if you release the pressure too fast, it will slush up in the bottle or can. If it's in a bottle, it's not a big deal because you can squeeze the bottle and get it out. If it slushes in the can, you can stick a straw in it and sip it but it's hard to squeeze out!