Laundromats are located throughout Japan and not only by travelers, but also used by local people. As same as in Europe, there are washing machines and dryers equipped inside the laundromats. By the way, Japanese word for laundromat is COIN LAUNDRY.
Normally most of the homes have their own washing machines, local people bring their blankets or other larger items which cannot accommodate at their washing machines. Dryers are heavily used during raining season; mid June to end of July, due to Japanese prefer to dry their laundries outside.
Laundromats are usually non-staffed, mostly hard to see any English information but the how to use the washing machine and dryers are same as in US or in Europe. The machines accept only coins but change machine is located inside the laundromat.