A comma ( , ) is a piece of punctuation used to show separation.
Anytime you speak directly to someone and address them by name, you must set their name off with a comma.
If you say their name first, you must put a comma after their name.
Bob, I hope we can do some golfing on Saturday.
If you say their name last, you must put a comma before their name.
I hope we can do some golfing on Saturday, Bob.
If you say their name in the middle of the sentence, you must put a comma on each side of their name.
I hope, Bob, that we can do some golfing on Saturday.
Do not use a comma with a name when you are talking about someone.
I heard that Bob is meeting us at the golf course on Saturday.
Only use a comma with a name when you are speaking directly to someone.
Bob, we will meet you at the golf course on Saturday.
Use a comma before or after or on both sides of a name when you are speaking directly to someone – when you are calling them by name.