This Japanese Guide page was written by me.
Another major difference between Japanese and English is that Japanese utilizes different levels of speech, using honorifics, different words, polite-level verb conjugations, etc., depending on how formal or casual the situation is and how you rank to the person you're speaking to. This means that in Japanese, there are many different ways to say the same thing, and the way that's used depends on the situation. Japanese people speak very differently when talking to their close friends and family as opposed to talking to their boss or teacher. But this is also what makes Japanese a more "intimate" language compared to English.
There are 3 polite levels of speech in Japanese. The lowest is "keigo," which is also the most common and universal. "Keigo" simply incorporates the constant use of "desu," the -masu form of verbs, and certain other polite expressions. The majority of Japanese learning books, as well as most sample sentences in this guide, teach using "keigo" because it's the most appropriate, especially for foreigners. Above "keigo" are "sonkeigo" and "kenjougo." "Sonkeigo" is a honorific way of speaking in which you "elevate" the rank of the person you're speaking to or about way above your own. "Kenjougo" is a humble way of speaking in which you humble yourself or "lower" your rank below the person you're speaking to. "Sonkeigo" and "kenjougo" are only used in very formal situations, such as formal business meetings, an employee speaking to a customer, or a servant speaking to their master. But for most situations, "keigo" is the best choice.
Japanese honorifics are short "suffixs" added to the ends of names in order to imply status and relationship between the speaker and the person being spoken to. There are many different honorifics, but here are some common ones:
-san = "-san" is probably the most common honorific and it's used equally for men and women. It's used in most situations that are not casul and can be added to either first names or last names. It's usally translated into English as "Mr.", "Ms.", or "Mrs." but it's used much more often in Japanese than those titles are in English. "-san" should definitely be used for anyone who is not a casual friend or close family member.
-chan = "-chan" is usually used by girls and women, or sometimes young boys. It's used to denote love or affection, either to close female friends or to something cute and little, like an animal or a baby. The only time a man might use "-chan" is to show affection towards a younger girl. "-chan" can also be used to make cute "nick-names" for very close friends, but it shouldn't be used for anything but very casual situations.
-kun = -"-kun" is used to show affection to a close male friend or a younger boy(similar to "-chan" for a girl.) But it can also be used for someone(either male or female), of a lower rank or social status. And like "-san" it's used for both first and last names.
-sama = "-sama" is a more polite form of "-san." It's used to show great respect, usually to someone of higher rank.
Honorifics are only one way to imply relationships in Japanese. There are many ways to say "you" and "I" in Japanese and, like the honorifics, each way implies a different level of speech even though they all mean the same thing. Here are a few examples of the different forms of "you" and "I."
I
Watakushi = very formal
Watashi = formal
Atashi = female speaker only(informal)
Boku = male speaker only(informal)
Ore = male speaker only(very informal)
You
Note: In Japanese, it's more polite to say the person's name or title instead of saying "you"
Anata = polite
Anta = a little less polite than "anata"
Kimi = casual(used for someone lower than you, or an informal equal)
Omae = very informal(unless it's used for very casual situations, it could be considered impolite)
Temee = impolite(you might as well say "Watch it, you're pi$$ing me off right now!")
Kisama = very impolite(you might as well say "I hate your guts and I may be about to kick your a$$!")
Just so you know, there are certain words and levels of speech that only men use, and would be inappropriate for women to use. Constant use of "ore," "omae," "temee," plain forms of verbs, no honorifics, etc., is "yakuza"(gangster) speech. You'll usually hear "tough" hot-tempered guys talk like this - nearly all guys in shounen anime and manga use "yakuza." However, it's extremely inappropriate for women to use this speech - in fact, it's usually inappropriate for women to use anything below "atashi" to refer to themselves, or "anta" to refer to others. When in doubt, just refer to yourself as "watashi," people you don't know as "anata," and use "keigo." With that, you should be fine. Just don't go around talking like Naruto or Inuyasha unless you want to get glares or a punch in the face XD
As I discussed in the previous part of this guide, there are many different congugations of Japanese verbs, but the basic present/future tense form is the Dictionary form. The "-masu" form has the same present/future tense meaning as the Dictionary form, but while the use of the Dictionary form creates a casual level of speech, use of the "-masu" form creates a normal-polite level. The "-masu" form is attached to Conjunctive base of a verb and can congugate into five basic congugations. I've listed these congugations below and compared them to the Dictionary form of the same verb. The Dictionary form is in plain text, the "-masu" form is in italics.
Verb = aruku - walk
walk = aruku, arukimasu
doesn't walk = arukanai, arukimasen
walked = aruita, arukimashita
didn't walk = arukanakatta, arukimasen deshita
let's walk = arukou, arukimashou
To give you a better idea of the different politeness levels of Japanese speech, I've listed sample sentences below; first in English and then different ways of saying the same sentence in Japanese.
Note: The word for "you" can be eliminated in the Japanese sentences if it's already understood. Of course, whichever form of "you" that's used also affects the speech level of the sentence.
Eng.: What are you doing?
Jap. sonkeigo: Nani o nasaimasu ka?
Jap. keigo: Anata wa nani o shimasu ka?
Jap. casual: Anta wa nani o suru ka?
Jap. yakuza: Nani o shiyagare, temee?
Eng.: I'll wait for you at school.
Jap. kenjougo: Gakkou de o-machi-itashimasu
Jap. keigo: Gakkou de matte imasu
Jap. casual: Gakkou de matte iru