"Don't put your hand out the car window, it's dangerous."
"It's dangerous so don't put your hand out the window."
"Don't put your hand out the car window, it's dangerous."
"don't ~" 「〜しないで」
"put your hand out ~" 「〜から手を出す」
"the car window" 「車の窓」
["it's dangerous" 「危ないから」](https://eikaiwa.dmm.com/uknow/questions/6793/)"it's not safe" 「安全じゃない」も言えます。
"It's dangerous so don't put your hand out the window."
"car" を言わなくてもいけます。
You shouldn't stick your hand out the window when we're driving. It's dangerous.
Don't put your hands outside the car like that when the car is moving. It's not safe.
この場合、次のような言い方ができます。
ーYou shouldn't stick your hand out the window when we're driving. It's dangerous.
「運転している時は窓から手を出さないで。危ないよ」
to stick one's hand out the window で「窓から手を出す」
ーDon't put your hands outside the car like that when the car is moving. It's not safe.
「車が動いている時に、そんな風に車の外に手を出さないで。危ないよ」
to put one's hands outside the car で「車の外に手を出す」
ご参考まで！
オーストラリア 
カナダ 
