I hope that you get lots of answers, for "really" is my favorite word in the whole English vocabulary. Really! ( = Believe me) I can tell you one thing that I have learned: the two words are NOT always interchangeable. You can say "I REALLY love her." You cannot say "I VERY love her." (You have to say "I VERY MUCH love her / I love her VERY MUCH. / I REALLY love her VERY MUCH. One expert says that the last sentence proves that the two words are NOT exactly the same. The "really" wants your listener to believe you and the "very much" tells your reader how deep your love is for her.) P.S. Some language forums refuse to answer questions about "really." Why? Because there are so many different ideas as to what it means in a particular sentence. Sometimes it depends on what is in the speaker's mind. And, of course, it is impossible to know (especially in writing) what a person is thinking. I will end with three examples: a. I REALLY do not speak Chinese. = I absolutely do not speak Chinese. b. I do not REALLY speak Chinese. = Maybe I know a little bit, but I am definitely not fluent. c. The Chinese language is REALLY beautiful. = Some people believe that it is more accurate to use "very" in this kind of sentence.

to use the adverb "really" you are expressing the urgency and importance of a certain feeling or state of being. Examples: Jane really needs to find a job, or she will have to move out of her apartment. His meal was really delicious, no wonder the judges gave him first place. I was really tired after walking around New York all day. "Very" is an adverb that adds some emphasis to the verb or adjective that it is paired with; we use "very" to let people know that something is above an average rating; that it is very good, as opposed to plain old average good. Examples: The teacher was very angry with Jason, you could see his face turn red. Pulp fiction is a very original movie. In Canada, the winters are very cold, so you better be used to freezing your butt off.