The "My Bookmarks" feature allows you to bookmark the page you're currently viewing by clicking on the "Mark" button. It will be saved to your personal My Bookmarks and be visible in the left column with the default wiki page name.
If you'd like to give the page a brief, more personal, description, you can type that in the text entry box before clicking the Mark button.
You will also find "Bookmarks" within the "My Account" section. Here it's not a particularly friendly feature to use; you have to know the page name of hthe page you want to book mark, type it into a box and click the add button. Both mechanisms maintain a single list of your personal bookmarks within TRP.
The feature is relatively rudimentary compared to the features found within some Web Browsers. But it meets a need within TRP of allowing individual users to create their own quick links in the left navigation menu.
Move your mouse over the title "My Bookmarks" in the left navigation column and the "toggle" icon will appear to the right of the title. Clicking once on the toggle icon will expand the feature; clicking again will collapse the feature.
Unfortunately the "My Bookmarks" in the left navigation column does not improve on the usability of bookmark folders and you are advised against using this part of the feature.