I think they give you guidance. I heard some of the process on a recent one. I don't catch it regularly but really like the ones I have heard.

use professional coaches to prepare their pitch.

Also moth radio people help polish the stories before presenting.

Most of the stories are compelling and compassionate with a sense of place and humor.

Pre-covid, we went to (but did not participate in) a bunch of the local Moth Story Slams. They're so much fun! At least here in Madison, WI, there were usually more people wanting to participate than there were time slots, so they threw names into a hat to select participants. I think the local Slams are the best way to work the kinks out of storytelling, and I believe those then feed into the larger Slams and the possibility to have a story played on the radio show.

I'm sure that's not the only route there, but a great way to learn the ropes!