Goals for the exhaust port are similar to those we achieved with the intakes: To reduce restriction to gas flow, but your methods are going to be a bit different.
Exhaust gases carry combustion by-products, of which carbon is a component. Over time, carbon deposits build up on the exhaust port walls and that can impede exhaust flow. To make the port walls more resistant to carbon build-up, in the final step you will give the exhaust port as smooth a texture as possible, a "near-mirror" finish, if you will.
The initial exhaust port work is very much like what you did to the intakes. The major part of the finishing and polishing will often be done with small-diameter, straight and tapered cartridge rolls. Do the port exits, bowls and valve guide work just like you did on the intakes.