You have just upgraded to a new iPhone and now it is time to set it up. That used to mean that you had to back up the data from your current phone via iTunes or iCloud. Then you must remember how you have configured the settings on your current phone and repeat those steps on your new device. Finally, you need to restore the backup of your data from your current phone to the new one via iTunes or iCloud.
With Apple's Quick Start feature, there is an easier way to set up a new iPhone. Introduced in iOS 11, Quick Start offers an automatic installation function for fitting a new iPhone. Just point your new phone at the current one and all core settings are transferred.
You still have to go through the installation screens for Face ID (or Touch ID), Siri and Apple Pay, but Quick Start takes care of the rest.
And there is more. With iOS 12.4 or higher on both phones, you can transfer your data directly from your current phone to your new device, wirelessly or via a wired connection. This means that you no longer have to back up your current phone in advance.
Transferring data wirelessly is the simpler option because you only need to make sure that the two phones are on the same Wi-Fi network and then to each other. Transferring the data via a wired connection requires both a Lightning-to-USB 3-camera adapter and a Lightning-to-USB cable, so that option is slightly more complicated and more expensive if you don't have the required cables yet has.