Confused about Data connections

[MacmanA4]

Hello Audi forum. I recently bought a 2016 A4 Avant. So far I love it, however I am completely baffled by all the different options for linking my car to the internet.  Carplay works very well with my iPhone 13. The phone works nicely through Bluetooth, but I don't understand all the other data connect options. I have tried in vain to get the car to connect to my iPhone to reach the internet. Audi told me I would need to replace MMI system to connect due to the age of the car. OK..... I did buy a PAYG SIM card and popped it in. OK that was fine, except I discovered that I would also need to pay for a subscription to some data services. It seemed to become a wi-fi hotspot. But I don't need a wi-fi hotspot as I have my iPhone on 5G, and it's paid for by work so... I took it out again. I'd like the car to just use my phone to access the internet.  So each time I start the car it annoyingly asks for a SIM card, and then tries to go to the Audi Connection manager. Can anyone share with me a bit of an ABC of what all the data options are for?  The manual is a bit hard to digest.  Audi have linked my car to me, and I have a Link Vehicle message in MyAudi App asking me to enter the 8 digit PIN shown there into the MMI system. What is that for? How do I do that?