You're allowed to delete five apps that come with your Mac, including Keynote, Pages, Numbers, GarageBand, and iMovie. For the rest of pre-installed apps, Apple regards them as parts of the operating system, leaving you no chance to delete them. If you're tired of seeing them on your desktop, you can quit them from the Dock. Just right-click the app > select Quit from the dropdown menu > then it will disappear from the Mac Dock.