Transferring contacts from iPad to iPhone se

Ensure that all of your devices are signed-in to iCloud with the same AppleID - then enable the Apple services that you would like to synchronise between devices on each.

For example, for Contacts - on both your iPad and iPhone:

Settings > [Your Name / AppleID] > iCloud > [Apps Using iCloud] Show All > Contacts -set to ON

Additional information can be found here:

Sign in to iCloud on all your devices - Apple Support

Activate "Contacts" from the iCloud options, and check that you are logged in with the same account on both devices.