David and Euan covered some of the new features in IOS 13, common to both iPhone and iPad, starting with Dark Mode. Icons now give short cut menus to app features and several apps have been given major upgrades e.g. Photos both as a data base and photo editing, Maps with much more info, Reminders and Mail with its new format bar, fonts and drawing.
All of this is detailed in two Books available free here for Apple Books: iPhone User Guide for IOS 13 and iPad User Guide for iPad OS. [Be sure to click the 'Books' link, not 'Web'].