To join the novice network, a mentor has to invite you. If you /shout in a city politely asking for an invitation, someone will likely send one.

Despite people who would try to deprive you of what is potentially a great tool for quick access to information, there are mentors who answer game questions as soon as they see them. It's definitely a good idea to join. If you join and find that you happen to be on a server where the NN is spammier or more political than most, set your chat filters so that novice only prints to one of the tabs you don't look at often, so that you can free yourself of the spam but still be able to switch to that tab if you have a question that needs a prompt or current response.