How do I use my iPhone cellular service on my iPad

If you have a cellular (not wifi only) iPad and your wireless provider supports

iPad data plans, ask your wireless provider for the appropriate

data only sim. Be advised there may be a monthly charge for this service.

If you are trying to use your iPhone as a hotspot to provide wifi

access for your iPad, you need to see if your wireless provider offers

that and if your account is properly provisioned (may also be a charge).

Here is a link to an Apple article on setting up a HotSpot:

https://support.apple.com/en-us/HT204023