youtube is your friend. a lot of the crazy combos you see on there however are from the beta where combos were obscene. But i learned a few sub zero combos i would have never thought of. Just type in mk9 (character) combos. the videos may not show you the buttons to do them but it will show you what youre capable of. another thing to remember is that with most characters combos you can input them very fast and give yourself a second to kinda set up for the next strikes.
example: with sub zero i hit back x y very fast then down forward a even though the combo is still going on because i did his ice blast right after it will automatically do it. then i hit y x y back forward b+rt. this does a 3 hit combo and an automatic enhance slide. the whole thing together took a little bit to master but it does about 35% damage and is easy to pull off.
with some characters they can hit you a million times but not do a ton of damage ie scorpion(shut up fan boys he hits like a water balloon unless hes comboing). they key balance with character combos is that some people ie sub zero have smaller combos that hit harder and give you utility while others hit faster and hit more with less damage.
Not sure if this helps but i tried