WiFi Dummy Question...Any Experts Answer This?

OK...I am very unclear on even what WiFi is, even though I've read about it. I suppose all I need to know is that it is a wireless protcol and there are hotspots.

OK...so I just bought an iPhone. I have it set to join available WiFi networks. It shows 3 of them whenever I try to connect with Safari, but all have LOCKS on them and want you to enter a password. How do you join and get a password?

Thanks for explaining, I'm new to this Wi Fi thing..

Tom