Most launderettes have two options:
- do it yourself, and yes, the instructions are clear, and if they are not, someone (either staff or another customer) will help you. Take your own soap powder, it's usually very expensive to use theirs. There will be washing machines and tumble driers. You may have to wait to use them, as others have said.
- get a service wash, which is when your drop off your laundry, a member of staff does the whole thing for you, and you pick up your items, washed and dried, sometime later
Not all launderettes do service washes, and sometimes they are only available at set times, eg the staff are there between 8am and 4pm or whatever. It is worth finding out if your preferred site does service washes, if you want one, before you lug your duvet all the way there.