I don't really need them to know anything other than that for stutterers, sometimes words don't come out right, and it's not fully known why, and it can come and go at the drop of a dime. If they take interest, I can tell them some stuff about how I experience stutter specifically. But I think the first part is quite serviceable in making them get the salient points. It's like quickly explaining colorblindness - which I also have - like, in a straightforward simple way that doesn't take too long (the longer stuff like this goes, the more likely it is to get interrupted - I think that's my reasoning, anyway).