Behind, Back, Rear
noun
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."
うしろ
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? It's うし, which is also the reading for this word.
後ろに見える大きな山が、ふじ山です。
The big mountain you can see behind is Mt. Fuji.
車の後ろのシートにティッシュがあります
There is a tissue on the back seat of the car.
人々の後ろに一人女の人が立っています。
A woman is standing behind people.