If I am introducing my name to a business client, which of these are correct:
1. Hello! Myself John. 2. Hello! My name is John. 3. Hello! I am John. 4. Hello! This is John. 5. Hello! John.
Numbers 2, 3, and 5 are standard ways to introduce yourself (if your name is John!).
Number 5 is less formal that the other two, and requires a particular kind of situation to be socially appropriate. It also requires certain pronunciation features and probably nonverbal behaviors to seem conventional.
Thus, numbers 2 and 3 are the safest and most standard of the list.
We cannot use "Myself John" to introduce ourselves.
Numbers 2 and 3 are used all the time. You should learn those two forms first.
Number 5 would be comparatively rare, and it would represent either 2 or 3, with the other words elided (left out). It might be used when a person is meeting several people at one time. You can say #4 as well as #3 to identify yourself over the phone. A context in which #5 would be correct is possible, but so rare (and some might say far-fetched) that you can forget it. For normal daily situations, it would not be used.