Say who you are, where you are and who you are talking to. Everything below is drawn from the vocabulary and grammar already on this site — no situation has its own private word list.
The one that matters most is who you are talking to. In Japanese it does not merely pick between words, it rebuilds the sentence: これいくら？ and こちらはおいくらでしょうか。 are the same question asked of two different people. Change the audience below and watch every sentence change with it.
Who are you talking to?
敬体 — the です/ます forms. The safe default with anyone you do not know well, and what you should learn first. Neither familiar nor grovelling.
Each sentence is a frame filled with a word from the fields above. Open at the other two levels to see the same thing said to a friend and to a client.
Getting by
Greet
おはようございます。
ohayō gozaimasu.
Good morning.
ございます is the deferential form of ある. Politeness in Japanese is a verb ending, not a separate word. more →
Thank
ありがとうございます。
arigatō gozaimasu.
Thank you.
Present tense for something still happening; ありがとうございました, past, for something now finished. more →
Apologise
すみません。
sumimasen.
I'm sorry. / Excuse me.
Negative in form — 'it does not end' — because the debt is not settled. It also does duty as 'excuse me' and even 'thank you'. more →
Get attention
すみません。
sumimasen.
Excuse me.
The same word as the apology. You are apologising for the interruption before you make it. more →
Ask for a repeat
もう一度お願いします。
mō ichido onegai shimasu.
Once more, please.
お願いします covers any request whose content is obvious from context. more →
Say you don't follow
よくわかりません。
yoku wakarimasen.
I don't quite follow.
よく 'well' softens it: not 'I don't understand' but 'I don't understand well'. Hedging is politeness. more →
Transacting
Ask the price
ねじはいくらですか。
neji wa ikura desu ka.
How much is screw?
いくら asks a price specifically; いくつ asks how many. か marks the question — no word order changes. more →
Ask for a thing
ドライバーをください。
doraibā o kudasai.
screwdriver, please.
ください is the imperative of くださる, the honorific of くれる 'give to me'. The politeness is baked into the verb of giving. more →
Accept
はい、お願いします。
hai, onegai shimasu.
Yes, please do.
はい agrees with the statement, not the action — watch it after a negative question. more →
Decline
いえ、大丈夫です。
ie, daijōbu desu.
No, I'm fine thanks.
大丈夫です declines. Hearing it as 'no' rather than 'yes I'm fine' is a milestone. more →
Check you got it right
虹ですよね。
niji desu yo ne.
It's rainbow, isn't it.
The polite copula plus the same two particles. ね is the single most common word in Japanese conversation. more →
Finding your way
Ask where
流しはどこですか。
nagashi wa doko desu ka.
Where is sink?
どこ sits exactly where the answer will sit. Nothing fronts. more →
Ask when
何時ですか。
nanji desu ka.
What time is it?
Clock times take に when you act at them: 三時に会いましょう. more →
Ask if they have it
歯ブラシはありますか。
haburashi wa arimasu ka.
Do you have toothbrush?
ありますか asks about existence, which is how Japanese asks about stock. more →
Say what you need
バグがほしいです。
bagu ga hoshii desu.
I'd like bug.
が because ほしい is an adjective describing the thing. Same pattern as 好き and 恋しい. more →
Test it
45 questions from this situation. All three answers are real sentences — only one fits who you are talking to.
Greet — friends, family, people younger than you. Which one?
The words
Other ways to say it
Words in play that carry an alternative — a different register, or a synonym worth knowing.
ゼロzero— zero→ 零 rei · まる maru (reading digits aloud)