I'm relatively new to many features of this site, also, so my guidance may be less than perfect. This is the message board. You can post a reply to any thread (topic) or start a new topic of your own. I think many people seem to spend some time going through the topics that are already on the board, at least the first couple of pages, and if you read the ones of interest you can just jump in. The chat room I've only been in once. On the main forum page on the right (at least it's on the right on my screen) there are many things you can click on, inclduding the chat room. And then another page will open and give instruction of how to get into the chat. I've also learned of late it's a good idea to read through the forum rules.
Lots of people on this board I've seen with many similar physical problems to yours, so I think you'll find plenty of company, although none of us wants to be in chronic pain. I've only had one surgery, but it didn't help my pain. Been through a ton of procedures before that - injections, physical therapy, etc., and am having to make some peace with being in pain for the rest of my life.
Oh, the pencil on the top of your post means you can click on it if you want to edit your own post (like if you think of something you want to add or change, you don't have to write a new reply), and the X is there so that you can delete a post if you want. You can only do these things to your posts, however, not to others. But the moderators can also edit posts if needed. You don't have to have a signature - you'll see a list of things at the bottom of some peoples' posts like maybe a quote, or their diagnosis, medications, etc. You can put whatever you want but you don't have to put anything. Right now I don't have a signature.
Hope some of this helps!