When you click on a forum's name, you are taken to the list of threads it contains. A thread is a conversation between members or guests. Each thread starts out as a single post and grows as more individual posts are added by different users. Threads can be rated to show how useful or popular they are and may contain polls.
To start a new thread simply click on the + Post New Thread button (you will need the right permissions to do this).
Threads can be ordered in many different ways. The default is to have the thread with the most recent activity at the top. But you can easily change this ordering, for example to have the thread with the most posts at the top, or the highest rating. Simply click on the appropriate column heading at the top of the list of threads (Thread, Thread Starter, Rating, Last Post, Replies or Views). You can also reverse the sorting order by clicking the arrow next to the name of the active option. (Note that 'sticky' threads will always be at the top no matter how you change the viewing options).