Once you've installed Plex Media Server, the program runs in the background on your Mac so you can enjoy all its features. Through this app, you can manage all the multimedia files you have, as well as organize the different folders where they're stored. It's a must-have app for using all the possibilities Plex has to offer.
If you want to manage everything the best way possible, you'll have to create an account and use it on your devices to synchronize your library wherever you want to use it.
You'll need to download Plex Media Server in order to use this streaming service for your own files. It's an incredibly intuitive tool and it uses metadata from different open source libraries to complete the information about files that don't have it.