1. 表示選擇，意為“或”“還是”：

Is the radio off or>Would you prefer tea or coffee? 你喜歡茶還是咖啡？

Is he asleep or awake? 他睡著了還是醒著?

Are you going to America by boat or by air? 你到美國是坐船還是坐飛機？

You may go or stay, according as you decide. 是去是留由你自己決定。

Are you from North China or South China? 你是華北人還是華南人?

You can come now or you can meet us there later. 你可以現在來，也可以稍晚和我們在那里碰頭。

2. 表示一種否定的條件，意為“否則”：

Come on, or we’ll be late. 快點，否則我們要遲到了。

Hurry up, or you'll be late for school.趕快，否則你上學就要遲到了。

Dress warmly, or else you’ll catch cold. 穿暖和點，否則你會感冒的。

Be careful, or you’ll break that vase! 小心，否則你會把那花瓶打碎!

Cross the road very carefully. Look both ways, or you might be knocked down. 過馬路要非常小心，要看兩邊，不然會被車撞倒。

3. 可表示“要不就是”：

He must be joking, or else he’s mad. 他一定在說笑話，要不就是瘋了。

The book must be here, or else you’ve lost it. 這書一定在這兒，要不就是你丟失了。

4. 用于否定句中代替and。

He was not clever or good-looking. 他不聰明，也長得不好看。

比較：

They sang and danced. 他們既唱歌又跳舞。

They didn't sing or dance. 他們既沒有唱歌也沒有跳舞。

5. 用于習語

The work is more or less finished. 工作大體上完成了。

They consist of 1700 or more tribes. 他們由1700個或更多部族構成。

There’s just one or two details I want to make sure about. 你母親或是你父親會陪你去。

（來源：網絡）