how does having a very slighty rough cylinder wall help the rings seat better and most of all what does it mean for them to seat?

 

The "roughness" of the cylinder wall (if you call marks 10 millionths of an inch or so deep "rough") is in a criss-cross pattern (crosshatch) and holds very small bits of oil to lubricate the sliding rings. It also gives the rings the correct surface to seal against.

Seating rings means making them "very friendly" with the cylinder bore by having them wear away minutely as they conform to the bore shape and texture. Usually they seal a little better after they "seat". The bore surface also conforms to the rings a little.

Modern rings should seat very quickly if the cylinder bore is properly prepared for the specific type of rings used. Ring manufacturers are the best source for what type if finish is needed on the bore, IMO.