Question: How to edit a thread's title?

I've just posted my first thread, but unfortunately I forgot to enter the title properly. How can I change it?! Like this, no one will now what this thread is about.

Click "Edit" on the first post of your thread, and then there should be a button that either says "Go Advanced" or "Use Full Editor". That'll bring you to a slightly more in-depth version of the post editor, and one of the things you can do there is edit the thread title.