We have never used the self-service laundry washers/dryers on a cruise. We basically feel every single hour is precious to us, and we want to spend it cruising! I know many do use the washroom, we just don't feel the need.
On the other hand, we make quiet a bit of use of the ship laundry/dry cleaning service. We find their prices to be very reasonable (surprised to find that out the first time!), and the quality good. You can find a price list in the stickies, but really just look at your local dry cleaners prices and you'll probably be right on.
On one long cruise we just packed our clothes informally into the suitcases, rather than try to pack them so they wouldn't wrinkle. Then the first day we sent a lot out for pressing. Came back the next day, looked like new, and we were set for the cruise. Since we like to dress nicely for the MDRs, but don't want to carry a lot of clothes, we will send out the first couple of nights' outfits to the cleaners to be ready to wear again later in the cruise.
They generally come back the next afternoon after you give them to the room steward. For an extra charge they have fast service, and for a extra extra charge they have same day service. The details are in the slip in your room, nothing you need to worry about now.
Dry cleaning/laundry is good quality, reasonably priced, and returned the next day. Another inexpensive option to free you up for more cruise enjoyment time!