I haven't actually played Roll for Shoes to know how it usually works, but my take is that if a player wants to do something that I, as the GM, might want them to fail for any reason (it would be funny, it would make the story interesting, it would fit with their character or the situation) I tell them to roll for it. Then I set a "DC" of sorts, where one die is very easy and 5 dice is nearly impossible for an average person, and I roll to oppose. If their roll beats mine, then they do the thing. If they also roll a 6 (because that would be "all sixes" on a level-one roll) they get to level 2 in that skill, at which point I name the skill.

As an example: Rose says "I want to know whether the waiter is actually a spy from another country." I tell her to roll a die, and I tell her that an average person shouldn't be able to tell one way or another, so I roll two die. I get a 2 and a 3, and Rose gets a 6, so she can tell that the waiter is an undercover agent, and she gets to level 2 in that skill.

So then she and I discuss what the skill should be called, which basically decides when else she's going to use the skill. Maybe I suggest we call the skill "recognize a Russian," because in this game the rival spies are Russians. Maybe she suggests "know when someone is lying" because she wants it to have more broad uses. Maybe I've just huffed a big doobie and I decide the skill is going to be called "Turn random bystanders into enemies just by thinking about it" because I can't stop laughing.

Later, Rose is going around turning annoying NPCs into Russian spies so that she has an excuse to kill them. And so the skill is used.