Wi-if n cellular capabilities for iPad Pro

1. eSim stands for electronic sim. Its a digital version of a cellular sim card. You would use it just like you would a regular sim card to get cellular service on an iPad. Except instead of getting a tiny little card you insert into the iPad, its setup directly through software in the iPad. Link-> Set up cellular data service on your Wi-Fi + Cellular model iPad - Apple Support

2. Wi-Fi calling is just what it sounds like. It lets you make cellular voice calls when connected to Wi-Fi if your service provider support the feature. The call is made over the internet. It is charged the same way regular cellular voice calls on your plan are charged. Do note, this only applies on an iPad if you have a paired iPhone. The iPad cannot place cellular calls or wi-fi calls on its own. Link-> Make a call with Wi-Fi Calling - Apple Support

An esim lets you activate cellular without an actual sim card.

Using Dual SIM with an eSIM - Apple Support

Wi-Fi calling is just that, calling over wifi instead of cellular.

Make a call with Wi-Fi Calling - Apple Support

It doesn't charge for data because it is using wifi service.

Allow phone calls on your iPad, iPod touch, and Mac - Apple Support