Just as a note: if for some reason you come back to it and find it isn't working for whatever reason. MK:X is Steam's first attempt at "streaming" game files for install. It failed pretty horrendously (why they'd use a AAA title to test it is beyond me).
As it stands, the workaround for it not downloading the files like it's supposed to is to click Mortal Kombat X on your library and just below the achievements bar you should see something like 29 files listed under "DLC" with check marks next to them to install. Check every single one of those if they're not. That will force steam to download them (they're not actually DLC, but game files needed for the thing to work).
That will get you at least to the main menu, where you'll find (if you're like me) you can do nothing except single fight and training mode. Although, access to the Krypt is available- and that would likely be the primary area a trainer would be useful in (unlimited koins). Either way, cheers.