Navy Vet here. Getting into the right forum is pretty straightforward. At the top of the site is a menu bar with "Forums" on it. Click on that and all the forums are visible. In each forum are threads, which are started by an original post and then the rest are replies. So, to find the right forum, look over the forums, which have names that describes what they are about. For example, under "MacOS" there are five forums, macOS - Operating System, macOS - Desktop Hardware, macOS Notebook Hardware, macOS - Apps and programs, and Running Windows on your Mac.
So you pick the forum most likely to cover your issue, then open the Forum and you will see all of the threads that already exist. To create a new thread with a new issue, just start typing in the top box where there is a faint "Thread title" prompt. That will start a new thread for you.
I think that covers it, but maybe one of the Mods will come along and add anything I left out.