Stock options during acquisition

[aim-high]

I got a new job offer recently with a startup company. They are offering me about 1000 stock options with the current market price of $10 per share. Those stock options vest 25% every year. So it will be 4 years before they are fully vested. What happens if the company gets acquired by another company down the line ? I have heard lot of people say that as part of acquisition they made so much money because of stock options. Can anyone explain with example what are different things that can happen during acquisition ?

Thanks