Arbital has a custom editor built specifically for creating Arbital pages. If you click the "Edit" button on any page, you can see the Markdown for that page and edit it if you have the right permissions.
The editor is split into five tabs: Title, Text, Relationships, Settings, and History. Everything under Title and Text should already make sense to you; if not, read Arbital page: Basics and Arbital Markdown respectively. If your screen is wide enough, the right half of the screen will have an instant preview as you type. If not, you'll need to hit the Preview button manually to see what the page's Markdown will look like rendered.
When you start editing the page, Arbital will store an autosave of your current state every 5 seconds. (Note that only the page's title, clickbait, and text is autosaved.) The autosave is overwritten each time. If you want to permanently store a version of the page, you can use the snapshot button, which is located on the left in the toolbar. Most other buttons in the toolbar are self-explanatory, and you can experiment with them to see what they do.
Nobody else will see the version you are editing, and as long as you continue editing it, it will remain locked so that nobody else can edit it. Once you are done, hit the Publish button to make your version go live and be visible to the public.
The Relationships tab contains all types of connections this page has to other pages. You are probably already familiar with parent-child and tag relationships. When you add or remove a relationship, that change is propagated immediately to the live version.