Speaking as someone who used to support OS/2:
Can someone tell me more about this os and what this os is primarily used for nowadays?
It's still in wider use than people think, mostly in the banking sector (many ATM's you use are running OS/2), but also in small random mission critical roles all over the place. Its continued existence is owed primarily to the fact that there is no clear upgrade path (i.e. "It works. It's paid for. I can't upgrade it. Leave it alone.").
How windows compatible is it?
Not very, unless all you run is Windows 3.1 apps (and even later Win3.1 apps didn't work well in OS/2 due to API changes made by M$).
(stops laughing). No.
If you're really interested, you can run OS/2 in a virtual machine from within Microsoft Virtual PC/Virtual Server.