Re: My friend John / My friend, John, went with me to the store.

Originally Posted by
bhaisahab
Both are correct. In the first one John is your only friend, in the second he is one of your friends.
I rarely say this, but I disagree with Bhaisahab. I would not assume that John was your only friend with sentence 1. We regularly use "my friend + name" without pauses or commas, especially when speaking. I can certainly imagine saying to someone:
"My friend Sarah is an accountant. My friend Bob is a teacher. My friend Dave is a thriller writer. His friend Bill makes horror films. So some of my friends have really interesting jobs!"
For me "My friend, John, went with me to the store" is simply a sentence which gives slightly more information than "My friend went with me to the store".
Remember - correct capitalisation, punctuation and spacing make posts much easier to read.