What is steam and like sites? Thinking of getting FlightSim

Hi There,

When it comes to video games I have only owned and played PC games.  Never had an XBox or PS.  I don't plan on getting one either.  I spend enough time on my PC as it is and I don't need to spend more time on other consoles.  Another thing is I'm so old school that all my games I have are retail version meaning, pop the disc in the CD-Rom to install and play.  Haven't bought a new game since GTAV came out on PC.  I miss those days going to Best Buy, CompUSA, Circuit City (though they were overpriced) and looking at the aisles and shelves of games.  So many games they divided it up into categories (Simulation, Action, Strategy, ect).  Looks like a lot of games now are bought online through a digital key or something like that.  I remember for most games having to type in an activation code number/letters after installing the game.  Not sure if that is still a thing. 

Anyway I was looking into getting Flight Simulator 2020.  I've played MSFS 2002, 2004 and bought, still have, but never really played FSX which is the 10th installment in the series.   Looking at reviews and YT vids it looks really good.  It seems the only best way to get it is through Steam or XBox Wire.  On the MSFS website they seem to push the XBox version which you can purchase for PC I guess.  Not to clear on how that works.  I see a lot of you play GTAV (lspdfr) through Steam.  From what I can tell Stream is a site where you can buy games digitally and play but you have to play it through the Steam software?  I'm just trying to figure what is the best way to buy, install , play FS 2020 and I'm not familiar with how Steam or Sites like it work.  If you all could explain how it works, that would be great!  Anyone play FS2020 on PC?  How did you go about it.