What is this ? and my guess

[html20009876]

Hi friends,
I can not find answer in google ...

Newbie questions about css formats:

1. #myMenu ul li a {....}
2. #myMenu, #myMenu ul {...}

3. #myMenu > li > a {...}
4. #myMenu ul li:hover a {...}

I guess that:
1 stands for "a of li of ul of #myMenu"
2 stands for "#myMenu and ul of #myMenu".

I totally don't know what 3 and 4 stand for.

Please help and explain.

Thanks.

.