Ok, thank you for the link.
So if I am using the Arctic theme,I still use the WordPress editor to add pages and to edit the pages or can I add and edit directly in Arctic theme?
You can add pages, posts and menus the same way you do with the default WordPress theme/setting. 🙂
For pages: WP Admin Panel > Pages > Add New
For posts: WP Admin Panel > Posts > Add New
And for you to see your newly created page on the menu, you add your page on the menu list via Appearance > Menu and find the menu the theme uses.
Leo’s provided link does well in explaining how to do this. https://docs.generatepress.com/article/using-the-wordpress-menu-builder/