How do you delete apps no longer needed on your computer?

It depends upon the app and the operating system version you are using. Some Apple ones can't be deleted but you still can on earlier system versions if you are determined. On later systems they are considered essential (but some aren't really) and you can't easily delete them. The simplest third party apps you can drag to the Trash. Some apps come with uninstallers, or an uninstall feature as part of their installer.