How does a lens hood and circular polarizer work together?

Ok i'm about to go all out and buy a circular polarizer for my 14-45mm lens for when i go trekking in nepal.

How does a cpl work in practice?

Firstly i was gonna get one without a front filter thread (for cost reasons). If i do and therefore cannot attach a lens cap when it is not in use, do i have to take it off when i put my camera away? Are there other solutions?

If i was to put my lens hood on then how does one turn the polarizer to the right strength? reach into the hood?

Do you need a lens hood with a cpl?

What am i missing? something obviously...

Thanks

David