Punctuation are small marks used to break up a piece of writing into more easily understandable chunks. There was originally no punctuation in Japanese, and what exists came from European influence, so it shouldn’t be especially mysterious. That being said, we’ll cover it for good measure.
The Period: 。
The Japanese period, called a 句点（くてん）formally or a 丸（まる）informally, works very similarly to its English counterpart. Periods are used to show that a sentence or thought is ending. The only significant difference to note is that Japanese periods are omitted when a given phrase occurs within quotes.
X 私はリンゴ、を食べた。I ate, an apple. (don’t use commas before particles)
O 明日、予定がありますか？ Do you have plans tomorrow?
Single Quotation marks: 「 」
Although these quotation marks look different than those of English, they’re used in basically the same ways: to show that someone is speaking, mark something as being a quote or generally show that whatever is inside them deserves special attention.
信用して」と道化師は言った。”Trust me,” the clown said.
Double Quotation Marks: 『 』
Double quotation marks in Japanese are used to mark a quote within a quote, when someone speaking is reiterating what someone else has said. They’re also used with book titles.
村上春樹『神の子どもたちはみな踊る』Murakami Haruki’s “After the Quake”
(lit. “All of God’s children dance”)
”The doctor said, ‘if he doesn’t quit smoking, your husband might die’ and mom started crying,” I said, relaying the events of the hospital-visit to my grandma.
The Exclamation Point: ！
The Japanese Exclamation Point, referred to formally as a 感嘆符（かんたんふ）or a ビックリマーク（びっくりまーく）informally, is used just like our English one to show strong feelings. Just like in English, it’s used mostly in informal situations.
知るもんか！ Hell’ if I know! or Who the hell knows!
しっかりしろ！Come on! Get a grip!
The Question Mark: ？
The Japanese Question Mark, known formally as a 疑問符（ぎもんふ）or as クエスチョンマーク（くえすちょんまーく）informally, serves the same purpose as it does in English: showing that a given phrase is a question.
That being said, Japanese also has the particle か to fulfill the exact same purpose. Although the two are often used in conjunction casually, question marks tend not to be used formally. In casual writing a question mark may be used in place of the particle か.
お名前はなんですか？What’s your name?
春樹、もうご飯食べた？Hey Haruki, did you eat already?
The Interpunct: ・
The interpunct, the first really new punctuation mark here, is thankfully very straightforward to use. It is used for clarity, separating words that might be difficult to separate otherwise or could cause confusion if unseparated. Practically speaking, you’ll mostly use it when writing names in katakana.
スミス・ジョン John Smith
ノリス・チャック Chuck Norris
トレーナー・シャツ Sweat shirt (“training shirt”)
The Ellipsis: ・・・
The ellipsis, referred to in Japanese as the 三点リーダー（さんてんりーだー）, looks a bit different than its English counterpart but is used mostly the same. It might suggest that a thought is being left unfinished, that time is passing, or when information is being omitted.
Today’s guest, Mr. so-and-so, can apparently consume an entire melon-bread pastry in one bite.
(Rather than creating fake names/places to go with fictional stories, it’s common to simply use ellipsis or a pair of circles ○○ as a placeholder.)
“Why, huh?...” She said with a troubled look on her face. “If I had to say, I guess it’s just that I don’t really like you all that much.”