jonathan18: The Supercharger recognises the car so there’s no need to do anything special; billing will be linked to the ‘owner - ie the rental company - which should then logically add the cost of any charging you do to your own bill (but doesn’t always seem to do, going by posts above).
As such, the actual charging experience should be no different to anyone else - rock up, set your charging limit, press the button on the handle to open the charging port (or open it via the car’s screen), stick it in, and you’re away. (You can always adjust the charging limit or stop charging early if you want to.)
If they’re just providing you with the access card (the equivalent of a conventional key) then there’ll be no need to create a Tesla account.
Thanks! Good to know that I can just rock up and it'll just work. Will also have a chat with the rental car company to confirm - as an earlier poster mentioned they weren't charged for using a supercharger!