Have users automatically subscribe to forum...
 

I can't seem to find the setting that will automatically email someone when something gets added to a forum that they have started or responded to.

Thank you

In each user's settings there's a "Default Thread Subscription Mode" (under General Settings) that lets a user choose to automatically subscribe to a thread when they start it or reply to it. You can also choose to subscribe to a thread or forum using the "Forum Tools" or "Thread Tools" menu on the forum or showthread pages. Hopefully one of those is what you're talking about.