Sentences are written in the first person, second person or third person:
The first person is generally used when writing things like diaries and letters, where the writer wants to express his or her personal feelings.
The first person can also be used for writing stories, especially if the author wants readers to know what the main character is thinking.
The second person is not used as much, but is common in advertising brochures.
You will have a wonderful time playing on our sandy beach.
The third person is the most common and is used for things like newspaper reports and most stories.
When writing stories it is a common mistake to switch between the first and third person without noticing.