How to tell if the device is connected to the internet?

Go to the device's IP addres and then navigate to status > mlat network. If the logs have no complaints then you have internet connectivity

An OK log.

If there are errors, i.e. not connected or name error, then you need to setup the device for internet connectivity. Also make sure your device assigned IP address is a good one. If you still gate name errors then you likely have issues with your router's or ISPs DNS system. You can attempt to fix name errors yourself