I want to register a new ipad

There is no “registration” procedure. When setting-up your new iPad (or any Apple device) with your AppleID, the device is automatically associated with your AppleID account.

That’s it - it’s now “registered” to you (or more accurately, to your AppleID).

If you also enable Find My iPad, this ensures that the iPad remains associated with your AppleID - and if lost or stolen, the iPad can located and remotely wiped if necessary. This is the Activation Lock - that remains forever active until you remove it, preventing reuse by anyone other than you:

Activation Lock for iPhone, iPad, and iPod touch - Apple Support