While they may often be used interchangeably, "too" implies that something is more that one can handle, whereas "so" simply means "very much." "He is so loud." (He is very loud) "He is too loud." (He needs to be quieter) "It's so cold!" (It is very cold) "It's too cold!" (I need to go somewhere warmer or put on warmer clothes)

I assume you mean like "so much" vs "too much". In this case, "so" just means "very". But "too" means "excessive", you don't want that much; you think there should be less. "So" could be bad or good, "too" is bad 90% of the time (the exception being "he's too good at this/she's too pretty" meaning it's unfair. but it's still a good thing) For example: Wow, you brought so much food (maybe you can finish it) You brought too much food (we can't finish it and now some of it will go to waste) Hope that helps you understand.