How do I connect my iPhone internet to my iPad?

Hotspot via the iPhone: How to set up a Personal Hotspot on your iPhone or iPad - Apple Support

Another potential option here is a MiFi or Jetpack box from a carrier (names vary), which is a box providing a local Wi-Fi network using the cellular network for its internet connection.

Or a terrestrial internet service provider, or Starlink.

iOS and iPadOS updates require Wi-Fi or 5G connections, and not Hotspot.

On your iPhone go to Settings > Personal Hotspot, and turn it on so others can join. Then on your iPad go to Settings > WiFi, and select the iPhone. As long as you are set to the same Apple account on both devices you will not need to enter a password.