The most useful one would be "Arigatou gozaimasu." It's pronounced as "a-ri-ga-to-o go-za-i-ma-s". (It's NOT the most formal indeed; we can be more formal and polite by saying like "Kansya itashimasu" "Koujin no itari de gozaimasu" etc. but I don't think you'd need them any time soon :) Basically, when you speak to someone -you just met and don't know well each other -who is older than you -who is your teacher or boss, it's always better to be polite, which means you use "...gozaimasu". (or "Sumimasen" mentioned below.) When you speak to -your close friends -kids -your own family, you can go with "Arigatou" (without -gozaimasu). You can add extra appreciation by putting "Doumo" or "Hontou-ni" before "Arigatou (gozaimasu)" So it becomes "Hontou-ni arigatou (gozaimasu)" or "Doumo arigatou (gozaimasu)". When you just want to show light appreciation, "Sumimasen" would work in most situations. It's light appreciation but still polite enough. "Doumo" is also light appreciation, but it may sound too casual(therefore impolite) depending on the way you say it.

Yes, there are many ways of saying thank you. You can decide which one you want to use, there are no rules which say "in this situation you MUST use this one" and "in this situation you MUST use this one". Probably stick with something like 'domo arigatou' or 'arigatou gozaimashita' when people teach you something or do something to help you, especially when you don't know them or they are older than you. After you make friends you can just use 'arigatou'. A slang one is 'azassu' (people started saying arigatou faster and faster and it somehow turned into 'azzasu'), just don't start using that one all over the place or people might be offended, probably best to ask a Japanese. There's probably plenty of other slang versions and ways to say 'thank you' as well. With some practice you'll get the hang of how to speak to different people in different situations, good luck.

The most informal way to say "Thank You" in Japanese is: Domo, Pronounced: Doh-mo Use this for people who might open a door for you, after a purchase directed to a clerk or taxi driver, and everyday good gestures and favors.

Hi Aura. The most formal way of saying "Thank You" in Japanese is: Domo - Arigato Pronounced: Doh-mo - ardei ga-toe Use this when someone gives a gift or goes out of there way to do something important for you. Such as, makes a phone call for you when they don't have to. Helps you to plan an event for you to attend, pays for your dinner or anything that may cost them extensive time or money. For gift receiving always combine with a bow. Click the link in resources to learn the proper way to bow in Japan. Do not use this term for an everyday "Thanks" the receiver of the Domo-Arigato will feel that you have just over thanked them. An informal way of saying "Thank You" in Japanese is: Arigato Pronounced: Ardei ga-toe Use this when someone is curtiouse to your needs and or is a thoughtful gesture that requires a Thanks. Example: Your are reading a map and trying to figure where to go, someone stops by to help you point the best direction. They did not have to stop by and assist in the situation but did anyway. Example: You are on your way out of one of Japans busy coffee shops, someone stops you to point out that your cell phone is laying on the table. Look them in the eye and say "Arigato." However, arigato is also seen as a feminine term used mostly by woman to either sex. Foreigners can use in any situation.