what the usage of method start() in AbstractApplicationContext

I'm a spring user. and I start to read the source code of spring.

when I read AbstractApplicationContext, I found there's one method start(), I found that the method doesn't be called when ApplicationContext is initialized.

My questions:
1)what the usage of the method? according to the word's(start) meaning, I think it should be called before the ApplicationContext can work. but it doesn't.

2)how can I listen the event which applicationContext starting working? after reading the code, I found the method will publish ContextStartedEvent. but if I just initialize the context, the context still can work and don't publish event.I can't listen the event to track the start of applicationcontext.

:)