Forgive me if this seems to be teaching grandma to 'suck eggs'. I find it easiest to assume lack of knowledge - I know I appreciate it when I am not sure of a subject, and I don't feel insulted when someone is trying to help...
I see what you mean about the CP User - there is not obvious way to add to the list. However, I use the favourites option. Open the forum index you want to read regularly [eg 'Computer-Internet Issues']. Then go 'Favourites', 'Add to Favourites', click 'New Folder', add name for this folder [eg, 'PPrune'], Then click 'OK'.
You have created a new folder [PPrune, which contains the hyperlink to Computer-Internet Issues]. It is positioned at the bottom of the 'Favourites' list. Scroll down to the end of Favourites, left click and hold, and scroll the folder up to the place where you want it to appear - somewhere near the top? Then when you open the browser, click on Favourites, the PPrune folder is right there in front of you.
Now go on to the next forum you view regularly. Repeat the process above, except you don't have to create a new folder - you add to the existing PPrune folder. And so on.
Then, when you have finished, you will have all your routinely read forum hyperlinks all lumped together in one folder.
I have found it the simplest and quickest way of switching between my favourite forums.