First, let's memorize this kanji:

後

In most cases, it means "behind," "after," or "later."

One of the first words containing this kanji that books teach is:

後ろ
うしろ
back (of something); behind (something)

But this reading 「うし.ろ」 is the least common of the kanji's three most common readings, the other two being ご and あと.

When attached to a word (usually the end of a word), it's pronounced ご. Like in this word, which you absolutely must memorize:

最後
さいご
the last; the end
Literally: "utmost (最) + after/behind (後)."

The reading we're looking at, though, is あと. This is an extremely common word:

後
あと
later; after

後 is best friends with で.

By adding で, you can make entire sentences like a boss:

A)
部屋掃除しなさい！
へや　そうじ　しなさい！
Clean your room!
Literally: "room + cleaning + do [command form]."

B)
後で。
あとで。
(I'll do it) Later.
Literally: "later."

If you're feeling extra fancy, you can include the verb that is getting left out in the above example:

後でやる。
あとで　やる。
I'll do it later.
Literally: "later + do."

Sentences like this are super common. Unfortunately, they're also super casual... which means they won't show up on the JLPT. The stuff they call casual on that test is always at least moderately polite.

As such, the N5 grammar using 後で is slightly more complicated...

JLPT N5: 後で（あとで）

The grammatical use of 後で that shows up on N5 does not mean "later." Rather, it means "after."

For example, if we want to say:

Would you like to go to a movie after class?

Then in Japanese, we would say:

Class（の）後で、would you like to go to a movie?

What's with that の？

Well, that's the thing. This usage of 後で will always come after either a noun or a verb in the plain past tense:

NOUN + の + 後で
Ｖた + 後で

So if we have a noun like 授業 (じゅぎょう // class; lesson), then it would be:

授業の後で
じゅぎょう　の　あとで
after class

And if we have a verb like 《シャワーを》浴びる (《シャワーを》あびる // to take a shower // Lit. "shower + を + bathe/shower"), then we put it in the plain past tense, 《シャワーを》浴びた (《シャワーを》あびた // took a shower):

シャワーを浴びた後で
シャワー　を　あびた　あとで
after taking a shower

Does that make sense? If not, you probably need to learn how to conjugate verbs in Japanese. We'll (eventually) talk about mastering that skill in one of our Sunday lessons, which we use for teaching structural aspects of the language.

Let's get down on some examples...

授業の後で、映画に行きませんか。
じゅぎょう　の　あとで、　えいが　に　いきませんか。
Would you like to go to a movie after class?
Literally: "class + の + after, + movie + に + won't go + か."

夕飯はシャワーを浴びる前に食べますか、浴びた後で食べますか。
ゆうはん　は　シャワー　を　あびる　まえ　に　たべますか、　あびた　あとで　たべますか。
Do you eat dinner before you shower or after you shower?
Literally: "dinner + は + take a shower + before + に + eat + か, + took a shower + after + eat + か."

☆☆☆ Vocab Tangent ☆☆☆
I used to get really mixed up about how to say "dinner" in Japanese. The reason is that there are five common ways to say it:

夕食・夕飯・晩ご飯・夜ご飯・ディナー
ゆうしょく・ゆうはん・ばんごはん・よるごはん・ディナー
dinner

Why are there five words? I have no idea. But all of them are pretty common, so feel free to use whichever one is your favorite. Rei and I seem to use 夜ご飯 a lot, but really that's just a personal preference.

If you're extra lazy, then go ahead and use the katakana version, ディナー, but personally I think that's no fun at all.
★★★ End Tangent ★★★

Oh, and we don't always need to write 後で in kanji. Sometimes people will just use hiragana:

お母さんが出かけたあとで、こっそり遊びに行こう。
おかあさん　が　でかけた　あとで、　こっそり　あそび　に　いこう。
After Mom leaves, let's sneak out and go play.
Literally: "mother + が + went out + after, + stealthily/secretly + play + に + let's go."
Note: To say "go to do (something)," we use the masu-stem of a verb (遊ぶ→遊びます→遊び) + に + VERB." If that sounds confusing, no worries. We'll have a lesson on it eventually.

Ready to level up?

The next point I'm going to make is something that I learned naturally from exposure to the language. But digging through my grammar books, it seems that I should have read about this a long time ago:

If the action in the second phrase is continuing, we remove the で from あとで and just say あと.

For example:

旅行の後、ブラジルが好きになった。
りょこう　の　あと、　ブラジル　が　すき　に　なった。
After my trip, I came to like Brazil.
Literally: "trip + の + after, + Brazil + が + liked + に + became."
Note: We don't put a で after 後 because (presumably) the speaker still likes Brazil.

Since the second phrase is a continuing action, the English translation will often be "since" instead of "after:"

私は仕事を辞めた後、両親と暮らしています。
わたし　は　しごと　を　やめた　あと、　りょうしん　と　くらしています。
I've been living with my parents since I quit my job.
Literally: "I + は + job + を + quit + after, + parents + と + am living."
Note: We don't put で after 後 because the second phrase is in present continuous tense, 暮らしています ("am living"). In other words, the action in the second phrase is continuing.

Being able to connect two phrases with あとで is crucial to becoming fluent in Japanese (as is pretty much everything in N5 and N4), so let's review... and review... and review... and master it!

Bonus Sentences:

後ろの方の席は空いてますか？
うしろ　の　ほう　の　せき　は　あいてます　か？
Are there any seats available in the back?
Literally: "back + の + direction + の + seat + は + are open + か?"

プリズン・ブレイク最後までみた？
プリズン・ブレイク　さいご　まで　みた？
Did you watch Prison Break all the way to the end?
Literally: "Prison Break + end + until + watched?"

夕食の献立が決まらない！
ゆうしょく　の　こんだて　が　きまらない！
I can't decide what to make for dinner!
Literally: "dinner + の + menu (for a specific meal) + が + won't be decided (→can't decide)."

晩ご飯、何がいい？
ばんごはん、　なに　が　いい？
What do you want for dinner?
Literally: "dinner, + what + が + good?"

きょう夜ご飯なにー？
きょう　よるごはん　なにー？
What's for dinner tonight?
Literally: "today + dinner + what?"

久しぶりに外でディナー食べようよ。
ひさしぶり　に　そと　で　ディナー　たべよう　よ。
Let's go out to dinner for a change.
Literally: "not for a long time + に + outside + で + dinner + let's eat + よ."