The first button means STOP. This is your lifeline if it all gets a bit uncomfortable and you feel the need to abandon your experiment.
The second is SPRAY. It… does what it says on the tin. You can see the WATER PRESSURE beneath the SPRAY and if you use this or the BIDET button you can use this to adjust to your personal requirements. There are some panels that come with options to adjust the temperature too.
FLUSHING SOUND is a bit stranger. Essentially, it’s there to prevent any embarrassment while you go about your business, and many cubicles come with automatic sensors that trigger the sound as you walk past. Before these were installed, the common practice was to flush before you get to work, and then afterwards to dispose of the evidence, which lead to a great deal of excess water use. The noise is there to cover up for you.
…I’m sure the POWERFUL DEODORIZER is self-explanatory and can be used at your own discretion.
TOILET SLIPPERS: In some places like onsen, ryokan and restaurants (essentially, anywhere that you’ve been asked to remove your shoes), you will find the establishment provides you with a pair of toilet slippers to wear. It’s more than likely that they’re going to be too small for you. They may or may not have the word TOILET emblazoned all over them, but this is to remind you to remove them once they’re done. UNDER NO CIRCUMSTANCES SHOULD YOU WEAR THESE OUTSIDE THE TOILET. Once you’ve made this mistake once and been shouted at by a scandalised Japanese granny, this is something you are never going to do again.
Take it from someone who knows.