If you live in Japan, I guess you have already used Washlet, or a modern toilet seat with bidet functions, and know well how to use it.
So this post is for someone who just arrived in Japan or those planning to visit here.
"Washlet" is actually a brand name of Toto Ltd. but everyone commonly calls this type of toilets Washlet, like Band-aid or Stotch Tape, no matter which company produces it.
I heard that a Washlet is installed in over 70 percent of Japanese
households today. It is very common in public places as well, such as
hotels, stations, restaurants and department stores.
OK, this is the one I'm using at home. It is not the latest model, but has all basic functions.
When you want to wash the anus, press the おしり （oshiri, or bottom) button, the second from the left. A nozzle comes out from underneath the toilet seat and squirts warm water. If girls would like to clean the different body part, press ビデ (bide, or bidet) button next to it, and the angle of the water jet will change.
To stop the water, press the left-most orange button marked 止 （stop). Don't forget. Never stand up before turning off the water, or the toilet floor gets wet.
After that you can dry the washed area with a blow dryer by pressing 乾燥（かんそう kanso, ｄｒｙ）button. However, I would recommend you the "conventional toilet paper method" because it takes long enough to dry the bottom completely and you might get cold.
You can adjust the strength of the water jet with the right-most 水勢 lever. Turn it clockwise (toward 強 meaning strong） to have more powerful jet, and rotate in the opposite direction (toward 弱 or weak) when you want it softer. Be careful, if the jet is too strong, some water gets into your body and makes you jump!
Today's useful Japanese expression:
トイレ は どこ ですか。Toire wa doko desuka? Where is the toilet (bath room)?
or more politely
おてあらい は どちら ですか。 Otearai wa dochira desuka?
Oteawai literally means the place to wash the hands.