How do I activate my new phone from my old one

See this support article:--> Transfer data from your previous iOS device to your new iPhone, iPad, or iPod touch - Apple Support

Regards

Giulio

If both have at least iOS 12, as soon as the new one is placed near the old, they should 'see' each other. The new will ask if it can copy the old's setup, while the old will ask for authorization to allow the new to do so.

Else, install the iTunes program in a computer (Mac preferred), use it to back up the old one into the local drive with password, then plug in the new one and tell iTunes to Restore the backup onto it. Same can be done with a newer Mac that has MacOS 15 Catalina by itself, no longer needs iTunes.