Click on "Settings" in the upper right corner, then "General Settings" under "My Account" on the left. On that page, you will find a "Default Thread Subscription Mode." Choose the mode you want, and save your settings ("Save Changes" down at the bottom.
If you only want to subscribe to certain individual threads, there's an option for that under the "Thread Tools" in the bar near the top of the thread. This will also work for threads that you haven't posted in.
Sorry, there used to be a Geocities web site where they had good versions of the chords for Split Enz and Crowded House songs, but it's not there anymore.