In your own words, explain the proper use of the comma to set apart nonessential elements within a sentence. provide a sample sentence to illustrate the rule.

The comma is used to give readers the signal of what is more important within the text or sentence. The information separated by the comma might be a description.
 
Example:
Dannie, my friend's dog, just passed by the park.

"my friend's dog" is just a description of Dannie but the whole point of the sentence is saying Dannie passed by the park.  So the information in the commas are not necessary.