Map drives outside of LAN

My Cloud OS 3 Personal & Network Attached Storage My Cloud EX4
1

I have the MyCloud EX4 all set up on my LAN and I can map drives just fine. But I cannot map the drives on a computer on another network. Is WebDav the answer? VPN?

2

explain a bit more on your network setup and someone can help.

3

I have the EX4 currently set up as a NAS Device but it is only accessible via LAN. It is hard wired to my google fiber router.