What does Roon do?


I'm an old tube guy and haven't really got a handle on digital, media streamers etc, although I do stream Spotify from my PC and iPhone to my hifi set up via a BluMe Bluetooth receiver / DAC. I keep seeing reference to Roon on this forum and its link with Tidal, which seems to be an alternative to Spotify. But what does Roon do and what do you need to connect it (if that is the right word ) to a preamp with no usb or HDMI ports, RCA only? Can you only use it with Tidal or can it work with Spotify? I need help in simple to understand language from you experts out there.
128x128mazian
Google is our friend, get yourself a general understanding and more specific questions will form. 
Maz, Roon's website is pretty informative and should easily answer all your questions. 
I have read what is on Google and the Roon website as suggested and it appears to me, as my equipment is certainly not Roon ready, I would have to replace a considerable portion of my system to use Roon. Not going to happen and I guess I'll stick with streaming Spotify  or perhaps trialling Tidal without Roon.