doglover, first
It's very easy to start a new thread, but you won't be able to start a new forum.
Choose the forum you wish to post in, such as this one is Plant ID Forum which is the correct place to find the name for a plant. Go to the bottom of the threads you can see on the page, there you will find you can put a title for a new thread and a post.
You may want to go to your profile, there is a tab at the top of the forums, on the bottom of the banner, for Profile, there you can change your site preferences. You can choose how many replies you can see on a page, this is convenient for those who have slow speeds as once the set replies have been reached a new page will be made in the same thread. For example, you set the number of replies or 'items' as it says to 20, after reaching 20 posts the next reply will be on page two. There's other options you can set there too.