Well, it goes Mortal Kombat: Mythologies (just back-story to MK1 and MK4), Mortal Kombat: Special Forces (but you can ignore this one), Mortal Kombat, Mortal Kombat 2 (MK: Shaolin Monks is pretty much an action game of this one), Mortal Kombat 3/Ultimate MK3/MK Trilogy, Mortal Kombat 4/Gold, Mortal Kombat: Deadly Alliance, and Mortal Kombat: Deception.

That's the roster.

I originally learned everything I know about MK from this http://db.gamefaqs.com/coinop/arcade/file/mortal_kombat_plot.txt on GameFAQs. Its a good resource for the new MK player. Be aware that this doesn't contain Shaolin Monks yet. And you need to use your discretion about what you accept as truth, since this just addresses what is definitely canon in the game. Personally I found that using this allowed me to learn what is true in MK, and form my own opinions based around that.