Please close the door behind you.
You must install the child carseat on the rear seat of the car.
If you turn around to look behind you and then do it again, you’ll see me.
The hiragana attached to this word doesn't suggest it's a verb or an adjective, so we can assume it's a noun. While 後で (you may or may not have seen this word yet) means "after," this one means all the other meanings you learned with the kanji: behind, back, and rear. Think of the ろ as a hint. It's like saying you're on the "road" (ろ) and you're driving so fast you're leaving everything "behind."
Since this word consists of a kanji with hiragana attached, you can bet that it will use the kun'yomi reading. You didn't learn that reading with this kanji, so here's a mnemonic to help you:
Continue to think you're driving on this road. You hit something, then look behind you, seeing you hit a cow. Know the word for cow in Japanese? You should. It's うし, which is also the reading for this word.