This is about conditioning rope made out of natural fibers. Don't singe nylon ropes! ;)
Conditioning is done to give the rope properties like a particular softness and look, and more durability.
Directly after you made your rope, and also after washing, it is a good idea to stretch the rope. Adjust one end somewhere and pull at the other end as hard as you can! If you are stretching your rope after washing or dying, it is required stretching it for a couple of days. This is also referred to as "drying under load".
The purpose of that is to even out the the forces in the rope, and the rope will stretch anyway, better it does not stretch too much when you have tied someone in it. If rope gets wet, especially hemp rope, it shrinks.
After you have twisted and stretched your rope, a good plausible next step would be singeing. That means holding it over a flame for a short moment to burn the little fibers that are sticking out.
The purpose of it is getting the rope "faster" because after singeing the rope is smoother and sticks less at itself and other things, like the clothing of your model. Furthermore it gets a nice shiny look without the little fibers looking out.
It is a very good idea to clean the soot away with a microfiber cloth afterwards.
Polishing rope is rubbing it at itself. To do it you fix a carabiner (or something else with a smooth surface) for instance at your balcony (outdoor is better), pull one end of your rope through and wrap it a few times around itself. Take the end of the rope in one hand and a rope piece about 40 cm away from the wrap-around-itself in the other. Pull alternately with your right and left hand. It will snow little rope pieces. Then you go a bit further on your rope and do the rub-at-itself with the whole rope.
Polishing rope means aging it artificially. If you would do 10 sessions with it, you would have the same effect (but more sweat). It makes the rope softer and prevents you from looking like you had a beige cat after your first ten rope sessions with you new rope.
To be added: boiling and waxing/oiling