So I thought I would give it a go at helping you.
Despite the ability to plug directly via an internet cable into your computer, you still need to do everything that you did before in setting up shares, Usernames, passwords etc., mapping the shares to a drive letter on the PC to access the shares on the Cloud. It won’t just show up as a hard drive like a USB drive would. The other difference is that now your computer is no longer connected to the internet, or if you are by using a second ethernet connection, then the Cloud won’t show up on the same network.
Assigning static IP to both devices is one way to get access but you don’t have to. If you left both devices, the cloud and your computer to dhcp, the default assigned ip to the Cloud is something like “the (auto) IP assigned to MyCloud is 169.254.7.48.”
If you do managed to figure out how all this works by plugging it directly to your computer, you might surprise yourself, once you figure out all this out because the only difference between plugging the cloud directly to your computer and plugging the cloud into the router, is the IP.
Now having said all the above, you still might be better off in getting a USB drive since the speed difference is enormous. If all the options of returning or selling it are closed to you and you still haven’t figure it all out, you might try optionally to remove the hard drive from the enclosure and use a third party USB 3 enclosure instead.
By the way, you don’t need any of the software in order to access a mapped drive. Un-install all the WD software that you did install and just learn how to mapped your Cloud to a drive letter on your PC or map a volume to a Mac.