Historically, there have been 3 ways to access a local share from the internet:
1. Port Forwading. On your router, you would setup access to the required ports to be able to see/access a share (file server of some sort, including a Time Capasule). Part of the process is forwaring the file sharing ports on the router to be accessible outside the firewall.
This can get fairly technical, as one needs to know the public IP address (typically of the router), which can change at any time, based on your ISP's needs and standards. One way around this is a service that shows you the live IP like
Dynamic DNS. Once DDNS is setup and you know your router IP, and all required ports are open and forwarded, it is possible to connect over the internet.
2. Use
Apple iCloud to allow remote access, at least for ATC devices.
3. Some third-party NAS boxes have an internet connection option that makes it easy to find the file server without needing to know the IP address, or configure any firewall rules (no port forwarding).
Synology QuickConnect is a good example of a vendor-specific solution.