Based on Rayette's offering a link I think it's safe to say that participating in a web forum is what's being asked about.
Having visited the website there are actually two forums hosted there, a public one and a private one due to the sensitive nature of the potential conversations themselves.
The public forum allows you to post as an unregistered guest. Once you activate the "Post New Topic" button you are presented with a web form (where you could log in if you have an account) but that by default shows you as user "Unregistered," offers a ReCaptcha (the audio version of which is a number sequence that's very easy to understand and spoken very slowly) to prove you're actually human, and the following fields and controls for your post:
I would have to presume that the private forum setup would be largely the same but that since login is required no ReCaptcha would be used. The preceding only covers posting, not reading, which is its own kettle of fish.
As Antony already noted, it's impossible to give truly generic instructions with regard to web forums, though there are several major formats that do get used repeatedly on different forums websites. If you intend to get heavily involved on a specific web forum it really is helpful to have a sighted assistant during the first couple of tries just so they can walk you through the controls that they see (some of which you may or may not need). Once you've got a given forum "system" down it's reasonably easy to use other forums that are using the same forums management software. It's also somewhat easier to plow your way through an unfamiliar forums software used elsewhere because you now have experience, and there are some strong similarities, though you may need or want sighted assistance to work through the differences.
Most online forum pages present lists of topics in the form of links, so using your screen reader to get a list of links is often a shortcut for getting a quick feel for what's currently being discussed. Some, depending on how they've structured the page, might also be categorized as headings, so using that element type can also sometimes be helpful. In the case of the particular forum Rayette shared the link to they structure their forums page such that threads are beautifully displayed as a list of headings, where the thread title is the heading. In NVDA the level 0 heading is the forum title itself and all the level 1 headings are the threads.
Here is a test to find out whether your mission in life is complete. If you’re alive, it isn’t.
~ Lauren Bacall