Welcome!
A thread is just basically a topic, to which people can respond with replies. Your post here is the original post of this thread and we are all replying to you. You can click on threads on the main part of the forum and reply to other's threads as well, should you find you have something you wish to say.
After you've submitted a certain number of posts (5 i think) you gain the ability to PM (private message) other forum members, which is analogous to email -- only they will be able to see and repsond to those messages.
That's about it! Check out some more info here:
http://www.soberrecovery.com/forums/...hat-users.html
I'm glad you found us!