Welcome to Photrio.
As far as navigation is concerned, I would recommend that you click on Forums near the top left to see the range of sub-forums available.
Then click on a few sub-forum headings to see the currently most active threads in those subforums.
In most cases, the site and threads are set up so clicking on a title takes you to the first post in the thread you have not yet read.
Many/most of us use the New Posts function to keep on top of things. Clicking on that gives you a list of threads that have new activity in them since you last visited. For that to work, you need to be signed in.
As far as the diagram goes, I thought first it showed the life of a moderator
.
But if it, as I suspect, is an attempt to put together the principles of film and print exposure, you might want to start a thread in the Black and White Film sub-forum (the really busy one with an explanatory title, some explanatory language, and your questions.