I have the full capability (NAV, embedded SIM, external SIM, Car Connect). Nothing vague about it.
1) Embedded SIM
At least for the 2018 718s, the car came with a year's internet connection via the embedded SIM. At the end of the year (or earlier, if you chose so) you had some decisions to make. My impression of the embedded SIM was that the connection was there, but it was slow and would act as a hotspot for one (1) smartphone/iphone via the Porsche WLAN. It gave internet connection to the NAV and some other silly Internet offerings (find Parking nearby, gas stations, Google Earth view and some others I never used). Also provides for NAV updates, although none was offered while the car is in my possession...
2) External SIM
You can choose to provide the car access to the internet with your phone acting as a hotspot. I did it, just to prove it to myself, but I chose the 'external' SIM card option. There is a slot for a 1/2" SIM card on the top part of the PCM unit. Any SIM card will work, you don't have to subscribe to the ATT card that Porsche is marketing. The hotspot provided with the external SIM allows you to connect more than one devices, something that proved useful in our cross country trip (i.e. my wife connected her MacBook Air and made reservations, searches etc, while I was driving with the CarPlay on.
3) Porsche Connect
Once you connect your phone to the Porsche WLAN via WiFi you can use the Porsche Connect app, a free app (different from the Porsche Car Connect app). Porsche Connect will allow you to use your phone to plan a trip, or find a destination and then pass it on to the car's NAV to navigate there. It can provide the capability to find an address with voice instructions and pass it on to the NAV with a complicated sequence, if you don't have Voice Commands activated in your car (it is a $0 option, but you have to request it when ordering, mine is a CPO and didn't have it). The alternative is to enter the address manually by typing on the screen, a process guaranteed to kill you, if you are driving simultaneously.
If you have an iPhone (I didn't and I hated that I had to get one), you can forget all the rigamarole with Porsche Connect and have a decent, voice command interface, activated by pressing in the left stalk, for voice commands. It works, and you can also use GoogleMaps and Waze. It works!
The biggest pain is accommodating the cable length that will make the plugging and unplugging of the iPhone painless (2+ ft). I solved this problem buying a cheap spiral cable from Amazon (make sure it has data capability, not just charging).
5) Porsche Car Connect
It is a subscription service provided by Vodafone. It provides some remote connectivity that allows you to see in your phone mileage, fuel remaining, range, current position of the car, way to go from where you are to your car, honk the horn, flash the alarms and set a GeoFence and a SpeedFence. There are a couple of other packages related to Security (something akin to LoJack) and Emergency Services, that I did not subscribe to. Cost is about $120/yr. I wanted this service because I spent considerable time in NYC this year and I left the car with the parking assistant. I wanted to make sure he didn't do a Ferris Buehler' Day Off with my Cayman.
The link to Vodafone is:
I hope that this helps, feel free to ask for clarifications, additional information.