Getting a network code/internet

First of all, I don't know much about computers. This might be a very stupid question, so I hope you all enjoy reading through it for comedic purposes.

I just moved into a new apartment with a few friends about a month ago. I have this computer that can pick up wireless networks so I can connect to the internet.

Every single one of the networks is locked and needs a password. I try connecting to my friends network, but he seems to have forgotten the password.

As I am on his computer now, is there anyway to find what his network password is, or is it something I have to call the internet company for to see if they can retrieve it?

Thanks for the help. This computer i'm on (his) is a mac. I don't know my way around a mac at all...any help is appreciated.

Jam it back in, in the dark.