How do I pair or sync iPhone to I pad?

Assuming that both the iPad and iPhone are signed-in to iCloud with the same AppleID, data can be simply synchronised between devices using iCloud:

Settings > [Your Name / AppleID] > iCloud - enable Apps and services as required

As for "pairing" (presumably using Bluetooth), what do you hope to achieve?

Whilst it is technically possible to do so, be aware that Bluetooth pairing between an iPad and iPhone is generally pointless. If your intention is to use Cellular Hotspot features of your iPhone, this link is optimally achieved using the native WiFi hotspot connection - this being a largely automated process. Hotspot connections over WiFi offer substantially greater throughput, range and reliability.

How to set up a Personal Hotspot on your iPhone or iPad – Apple Support

If you still wish to pair your iPad and iPhone over Bluetooth, you first need to manually enable the hotspot feature on your iPhone:

Settings > Mobile Data > Personal Hotspot > Allow Others to Join - set to ON

Next, Bluetooth for both the iPad and iPhone must be placed in Discovery mode:

Settings > Bluetooth (accessing this page will automatically place the device in Discovery mode)

Whilst both iPad and iPhone are in Discovery mode, you can mutually pair the devices.

Again, I must stress, unless you have an unusual “edge case”, pairing of iPad and iPhone over Bluetooth has no benefit.

You cannot pair an iPhone and an iPad together but you can sync them using iCloud. On each device, go to Settings > [your name] > iCloud > Show All and turn on the apps whose content you want to sync.