To post a new topic you have to enter the forum area in which your new thread will be relevant. Example, click on "Learning Photography" forum and then select a sub forum such as "Portrait". Once you are inside the Portrait forum and want to post a new thread topic look at the upper left of your page, just below the page header, and there is a yellow button that says "Post New Thread".
There is no one page that allows you to post a new thread to any particular area. the new question or topic you wish to start needs to be started inside the forum topic area it is relevant too.