Click on UserCP in the blue band at the top of the page and you will see your subscriptions. When you start a thread or post a reply you are automatically subscribed to it and a link to it will appear there.
Or just click on your screen name at the left hand side of this message and you get an option to view all your posts.
Or if there is a little blue box with a tick to the right of the thread name then you know you have posted in that thread.
There are helpful Tutorial and FAQ sections in the blue band at the top as well which will help you find your way around.
