Another noob question coming from me but what are 50/50s?
When you execute a move that has a 50/50 chance of succeeding. For example, if you time a launcher over a downed opponent hoping that he stands up into it when he could very well just use a wake up attack and knock you over would be an example of a 50/50. It's not always a 50% chance, but it's refered to as a 50/50 just the same.
FYI, I'm not sure if that will even work in MK considering wake-up attacks have invulnerability stages or armor that keeps them from getting hit. There is probably a more relevant example out there but i can't think of it. Either way it should answer the question.