Hi, thanks a lot for that quick answer. This whole trip is very important for me. I am from smaller town and travelling here is much easier

.
I read the site about Oyster card, I just couldn't figure out, how much I will pay for travelling with it.
I looked again and there is no underground to Watford Junction only Overground(
http://www.tfl.gov.uk/assets/downloa...t-tube-map.pdf).
Undeground goes to tube station called Watford but it is more than three miles far from place where I need to go. Watford junction train stop is really close so that is my plan A.