First, if you haven’t done so already, read the My Cloud User Manual (https://support.wdc.com/product.aspx?ID=904) which explains how to use the My Cloud and it’s features.
Second, the My Cloud already includes a media server called Twonky for streaming music, video, pictures. The My Cloud also includes an iTunes media server for streaming music to iTunes capable devices.
Third, one configures the My Cloud, including creating additional “Shares”, enabling/disabling the Twonky media server (and iTunes media server), enabling/disabling “Media Serving” on those Shares through the My Cloud Dashboard.
Forth, to copy files/folders to the My Cloud one typically uses Windows File Explorer or Mac Finder. One can make things easier by “mapping” a Share to the local computer.
Fifth, MiMim Server has a Installation (t) and User Guide (http://minimserver.com/userguide.html) that explains how to use that media server (if you haven’t seen it already).
https://support.wdc.com/knowledgebase/answer.aspx?ID=2686
If using the embedded Twonky media server it is recommended one read the following unofficial Twonky FAQ.
