Japanese is the main language spoken in Japan. Japanese is a subject-object-verb (SOV) language, which means that you say things like "I rice eat." On the other hand, English is a subject-verb-object language, because you say things like "I eat rice." Many Japanese people know a few words of English, but it really helps if you know Japanese.
The currency in Japan is the yen. Like U.S. dollars, the yen has both coins and notes. However, coins here are much more valuable. They even have a 500 yen coin, which is equivalent to $5! Therefore, it is much worse to lose coins over here, so everyone carries around a coin purse.
A bottle of water costs around 100 yen, or $1. You can buy them from vending machines, which are everywhere and serve water, energy drinks, juices, coffee, tea, and many other drinks. You can also buy them from convenience stores, which are open 24 hours and have everything you could possibly need for day-to-day life.