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.
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.
I was having dropouts streaming tidal thru my network using my laptop to control it so I bought the nucleus and now have a music server with a pretty cool os that consolidates my music( took me some effort) and allows to choose between my music or tidal. Roon also brings up album covers, lyrics, history and recently I started playing around with their dsp to smooth out some lumps in the bass in my room. You can install roon in a pc or a dedicated server. I'm using a nucleus driving a hegel dac or sooloos with impressive results, being more of a flip phone type it took me more effort than it should have but the system locates your sources, called zones, has you name them and then select which zone or zones you want to control.
I’m a long time tube guy too.

You need a PC to use Roon. Think of Roon like an operating system for your music, it knits together all your digital music, whether stored on a hard drive or bought on iTunes, or streamed through a high Rez service like Tidal or Qobuz (but not Spotify).

it won’t help you on your physical collections of cd or vinyl unless and until you transfer them onto a PC.

Roon aggregates all this music into one seamless interface, which you control and search and playback via a range of devices including your phone, iPad, or PC, which act like remote controls. It then let’s you play your music back, on up to six different systems, which can include playback on stand alone devices like your phone, PC, or iPad, or via gear like a receiver (if it supports Airplay), Sonos, or a Roon ready hardware device like a DAC. It supports over 40 different hardware manufacturers who are Roon-ready or Roon Tested.

I like like not being tied down to the usually crappy software apps that most manufacturers release (and then stop supporting after several years). I wish all hardware makers would stop producing apps and software and just leave it to Roon, who does a much better job.

it costs $120 a year or a lump lifetime fee of $499. Plus the cost of a PC to host it, if you don’t already have a PC or MAC or a dedicated server.

Roon isn’t mobile, meaning you can’t access it when you are away from your home network.

For me, a guy who wants to simplify and integrate all his music into one place, and easily discover it and play it back across all of my music systems at home (and those of my kids and spouse), Roon is a revelation. The ability to discover and experience new music and old favorites has made Roon the best music purchase I’ve made in over six years.
I tried Roon free trial for a week, using a MacBook Air.  It kept crashing.  I think it needs a lot of computer horsepower, which is why they started making their own hardware.
  I listen to Classical, and I didn’t find the information Roon provided of any value, and imo their suggestions were nonsensical.  And I am not a fan of someone suggesting what I listen to.  Ymmv
I actually use the Roon’s own Nucleus. It is an Intel NUC i3, which wouldn’t ever be described as a lot of horsepower, and the processing speed for basic DSP capabilities is pretty light. Roon built its own hardware mainly to address those audiophiles who didn’t want a DIY solution but rather the simplicity of a preconfigured solution. Nucleus plus is a NUC i7 which is needed only if you are doing heavy room correction DSP along with DSD upsampling to 512, or have massive libraries that need to be indexed.

not sure why you experienced some pain with your MacBook but it wasn’t due to not having enough compute power.