Transferring contacts from iPad to iPhone se

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

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