What plex software to use?

i am new in Plex. I do have a 'Roku SoundBridge Network Music Player (always used with Winamp&SOUNDcast or Internet-radio) and a 'Conceptronic NAS'.
My question:
What Plex stuff do I need to use to be able to select music on Phone&Tablet (with nice GUI) and send a command to the SoundBridge to play that music. I do understand I need a Windows-machine somewhere in the Network to Stream the music (Plex Media Server), But what software do I need on Phone and what on SoundBridge. Does someone has a drawing of such a configuration.