How do I get the trial and how do I cancel it?

To get the free trial, just connect to your vehicle and attempt to use any paid feature in the Carista app and you'll be presented with a purchase screen with 2 options. One of those options is for a yearly subscription and includes a free trial. Select that option and it will unlock all functionality in the app for the trial period.
You can find instructions on how to cancel your subscription here:

• iOS
• Android