If you are prepared to do something, you are willing to do it if necessary.
Are you prepared to take industrial action?
你们愿意采取劳工行动吗?
If you are prepared for something that you think is going to happen, you are ready for it.
Police are prepared for large numbers of demonstrators.
警察已做好应对大批示威者的准备。
You can describe something as prepared when it has been done or made beforehand, so that it is ready when it is needed.
He ended his prepared statement by thanking the police.
最后他以感谢警方结束他事先准备好的声明。