I don't use Apple technology so I'm not the best person to answer this. From the internet it appears that you can export your Apple Calendar appointments/events as an .ics file. This is a standard format used for transfer between calendar programs. You could then import the events into Thunderbird. However I'm wondering if that's really what you want to do. You talk about wanting to have your system on two devices. In that case, having the appointments only within Thunderbird (on your computer) won't achieve it. Since you've already mentioned Google, a better way forward might be to import the .ics data into your Google calendar online. You could then set up Thunderbird to show your Google calendar data on your computer. If your phone will also work with your Google calendar you would be able to see and manage your appointments both from your computer and from your phone. I hope this is some help.