"on" would be "it" or "you" like in "You could say it's a funny week" : on pourrait dire que c'est une semaine amusante. If I'm wrong, please correct my mistakes! ;)

"On" is a non committing "we". It could mean "all of us" or "just some of us" o2 "some people in general" and it doesn't want to be precise about which one it is. Just accept it as a slippery notion with no equals in English.

It's hard to explain. On is used often for 'we'. For example, on va ...... (we're going to.....) I think it is used more as a general we, rather than a specific one. Imagine the english phrase 'one will do this', I think the use of on is the French equivalent.