Are usernames and passwords that I type in while using Tor encrypted from the nodes? For example, I want to use facebook, but I'm not sure if my login information is protected while I use Tor.
Yes, the content that goes over the tor nodes is encrypted, but is not encrypted beyond the tor nodes. Beyond the tor nodes SSL should be enabled.
In either case if the site is using SSL it should be encrypted and not viewable to the nodes, even if tor wasn't encrypted.