PREP is a kind of method that helps you to claim your comments and statements that you want to let others know about it. If you want to write a article or something that you want to argue, follow this instruction and you would get a success. So, 'P' means 'Point' which is 'I think ~' then write or speak what you think first. Next 'R' means 'Reason'. You give them why you think like that. Then third, 'E' means 'Example' so you give them an example of your thoughts. And finally 'P' again means 'Point' so you speak or write your comments or statements or your thoughts ones more to emphasize your opinions.
Here is an example, "I think he is a bad person" it's 'P'-'Point' / "Because, he stole my laptop" it's 'R'-'Reason' / "I saw a news that whoever steals someone's staff they will call them a bad person" it's for 'E'-'Example' / "So, because he stole my laptop I think he is a bad person so don't play with him" it's again 'P'-'Point' at last. As you can see you can add some more words on the second 'P'-'Point' if you want!!!^^