To make your own thread-When you enter Forums from the main screen, choose Forums again (not Active Topics). There you will see all the topics available in forums (War, Strategy, Off Topic, etc.) Choose the topic that best fits your thread. Once you are in that topic, go to the top right hand corner, to a button that says New Post. That should allow you to create a new thread.
Wedding Wars-It's just a war created by two players who want to get 'PIMD married'. It's usually just an excuse to have a fun system war among friends and other players.