Syncing ipad and iPhone

iPad does not sync to iPhone. iPad syncs to a computer. iPhone syncs to a computer.

You may have the same data in certain applications on iPad and iPhone if that data is housed in iCloud. Or if, for example, you use the same email account on both devices and that data is housed in your email service provider’s server.

Both your iPad and iPhone must be signed-in to iCloud with the same AppleID. 

Sign in to iCloud on all your devices - Apple Support

Having signed-in to iCloud, you can enable services and Apps that you would like to synchronise between your devices:

Settings > [Your Name / AppleID] > iCloud

The iCloud User Guide provides comprehensive information:

iCloud User Guide - Apple Support