You can't add yourself to conversations. Conversations are between two or more people. If you're trying to post a public thread, you will have to go to the section you want to post in and click 'Create Thread' near the top.
Conversations are private and between select people only, threads are public for all to see and reply to.
go to any subsection, click create new thread, type what you want, then click create new thread at the bottom/top, wherever it is for you