My dog, a Bavarian Schnapper, is incredible stupid.
He bit the mailman, the plumber, and my cousin Snooky.
You may notice that the appositive in one of the sentences above is set off by commas while the other sentence contains no commas. If the appositive is necessary to identify the word which it follows, no commas are required. The name Snooky tells the reader which cousin the dog bit, so no comma is required. In the other sentence the words "a Bavarian Schnapper" are just extra words. The dog has been identified when the speaker says "my dog." (If the speaker had more than one dog, he would probably say "my Bavarian Schnapper" to distinguish between that dog and any other dogs that he owns.
Here are some more examples of appositives:
Aristotle Mongoose's great passion, chocolate chip cookies, was causing him to gain weight.
He went to a reducing salon, where he met Miss Sweetcakes, a charming lady.
They both had read the book, Love is Chocolate.
Mongoose decided that Miss Sweetcakes, a lady who appreciated the finer things, was the one for him.