In aleatoric music you leave everything to chance. The pitches are assigned to the specific numbers of the roll of the dice. You roll the dice and write the note that has shown up by accident. Roll some more and write another pitch. Twelve pitches of the chromatic scale - twelve numbers of two dice cubes. That's how it works.
There's one thing serial and aleatoric music have in common - they both sound exactly the same.
Cats love such music. Every time you see a cat on a keyboard - that's what they're using.
"Hey, Tigger, what are you playing?"
"I can't decide what I want to play - total serialism or aleatory".
"Can't you just compromise? Play serial aleatory or something."