OK, so firstly I state that my experience is for the MyCloud Mirror. I think the firmware etc between it and the EX2 is almost identical, but I include the statement just in case there are some differences I am not aware of in the specifics.
For terminology, the “public IP” address is the one that your ISP assigns to you, and unless it’s explicitly static it may well change over time (when you reboot your router for example, or when the ISP feels like it). This is the IP address on the internet that someone from outside will need if they want to get access to your router, and from there to your local network. Your ISP can make this address static and unchanging (for a fee) or you can use a DDNS (dynamic DNS) service like NoIP to do it for you (for free with some requirements such as renewing every 30 days or accepting advertising, or again for a fee without them). What that will do is give you a name (e.g. myfancyfixedIP.noip.com) which will always resolve to your dynamic public IP address, no matter if it changes or not. Look up DDNS on Google for more details, and for other providers (there are very many, I only mention NoIP as they are who I use as their service is included with my router).
On the local side, firstly you will need to enable WebDAV on your EX2 as you already found. Then for each share that you want to access, you also need to enable it there (it’s in the properties of the share, under the share menu).
Next you will need to give your EX2 a static IP address on your local network if it doesn’t already have one. This is so that your router will always know where it is. This can either be done on the EX2 itself or on your router (in the DHCP settings). Again look in the manual for details of how to do that.
Lastly you need to forward the WebDAV ports on your router (normally 80 and 443) to the IP address of your EX2 (hence the need for it to have a static IP address on your local network).
What will then happen is when you try to access your files/folders/shares from the wider internet, you use a suitable WebDAV client pointing at your public IP address (or the DDNS name equivalent) and the relevant port. You also need to include in the client settings the username and password, which will correspond to the required username and password on your EX2 to access the share you are trying to reach. The ISP (optionally via the DDNS) will then send the request to your router, which will pass it on to the EX2 due to the port forwarding. If the login credentials are correct it will then pass the file/folder list for the share back to you, and you can access your data.
WebDAV is an extension to the normal hypertext (http) format, hence why there are two ports. One (port 80) is for normal (http) access and the other (port 443) is for secure (https) access. Which you use is entirely up to you. It is also possible to use different port numbers on both the router (you can forward any port coming in to a different port going out of the router in this case to EX2) and the EX2 - in both cases this option is available in the dashboard when you enable the protocol.
Sorry it’s a bit of a long reply, but I’m trying to get over the whole concept. I’m sure there are more “walkthrough” details around on the internet if you do a search, or if you have more specific questions just post here and we can try and give you more answers and help.
