The Forum Tabs are the options you see in the yellow bar at the top of the screen. You'll see: Nurses, Specialties, Critical, APN, News, Students, Colleges, Degrees, Career, US, World, Articles, Jobs and Breakroom.
These options will take you to the list of forums that are within each category. For example, under the U.S. tab, you'll find a forum for each state. Under the Students tab, you'll find forums for pre-nursing students, BSN and ADN, LPN, NCLEX tips, etc. I highly suggest browsing through each tab to become familiar with the different forums.
Once you've found the forum where you would like to post, click on the forum title to see the individual threads that have been posted there. At the top of the list and to the right you will see a blue bow with white letters that says "Start a Topic Now." Click on that and select "New Topic" from the drop-down menu. You will then be taken to a page where you can write your thread and then post it.
Hint: It will be very similar to the way that you posted a topic here.
Since, you're new to the site, I'll mention the search bar. At the very top of the page, to the right there is a search bar. It's a greg idea to search your topic before you post it. Some topics are discussed very frequently and you might find that you can get the answer to your question by reading previous threads, rather than posting a new one.