Let’s start with an easy one. Most people are aware that you take your shoes off before entering a home in Japan. It’s a reasonable and hygienic request when you think about it. They simply don’t want the dust and dirt from the outside streets being trekked all over their clean floors and tatami mats.
Most homes have a small recessed vestibule called a genkan where shoes should be removed and slippers put on (guest slippers are often provided). Note, these slippers should be removed when you enter a tatami mat room, where socks are the preferred footwear.