CMSimple_XH has a specialty that makes it somewhat unique amongst content management systems: new pages can simply be inserted by making a new heading. This systems works like a book: a new heading creates a new chapter in the book, and in CMSimple_XH it creates a new page.
Overall there are 6 heading levels: h1 to h6. CMSimple_XH uses h1-h3 to structure the pages and the remaining h4-h6 to structure every single page. To stick with the book metaphor: h1 introduces a chapter, h2 a section and h3 a subsection.
Actually you can customize how many headings levels are used for separate pages by changing Settings→CMS→Menu→Levels. The highest permitted value for this setting is 6, but it is recommended that you use at most 4 or 5, to have further headings left to structure the content of a single page.
How to actually create and delete pages is described in another article.
CMSimple_XH is an online-CMS. Contents is stored in the file content.htm, page related data in pagedata.php. While saving a page CMSimple_XH synchronizes automatically content.htm and pagedata.php. You shouldn't edit content.htm nor pagedata.php offline in an editor, as you are likely to derange the sychronization.
Two plugins that save data in pagedata.php are part of the basic CMSimple_XH package: meta_tags und page_params.
Via meta_tags you can assign separate meta tags for every page, e.g. keywords, a different page title and a separate page description. These meta tags are important for Search Engine Optimisation (SEO) of your pages.
Via page_params you can, among other things, assign a different template to a page, exclude (hide) the page from the navigation menu, assign an internal or external redirection, etc.
If you edit the content.htm offline, you are likely to get out of sync with the pagedata.php. Typical results are that hidden pages aren't hidden any more but other pages are hidden, i.e. the pagedata assignments get shifted to different pages. Therefore usually you will not want to edit these files offline.
If however you wish to work offline on your CMSimple installation, you should definitely install a web server like XAMPP on your computer, what makes it possible to edit a copy of your CMSimple_XH site on your computer, which you can upload afterwards.