Google Analytics settings for subdirectories


I am installing google analytics for my sub-directories based Multisite. I am the only user for all the sites in my multisite. Should I re-enter the same UA-xxxx code for every site?

Also what does it mean “Admin pages tracking” and “domain mapping”? which is the difference between activating / de-activating it?

And finally: how can I see the google analytics statistics inside WP Dashboard? it says “login to google with the button above to enable this functionality” but I don’t know which button reffers to…

Thank you,