You can add the current page to your bookmark set by clicking on the Mark this page icon or use the keyboard shortcut Ctrl+D (⌘-D on Mac). It will add to the Bookmark list and you can also write some notes for it in the bottom of the panel, Bookmark notes. Selecting each item of the list will navigate you to that page, and you may want to remove that item by clicking on the Unmark selected icon . You can switch between your opened sets (default one and those you imported) using the combo list of opened bookmark sets below the panel toolbar. Once you close Kiwix, all your sets will be closed and you will need to import them again the next time.