Don't Be Fooled!
You cannot win a prize for a contest you did not enter.
REPEAT: You cannot win a prize for a contest you did not enter.
Because many of these scams originate from outside of the United States, English is often not their first language, and typically there will be misspellings and strange wordings in the letter.
For example, you may see congratulations spelled as "congradulations". Or you may see a strange wording such as, "We are most joyous to bring you good news!"
When you get an e-mail, note the e-mail address it came from, and where they want you to reply. A real lottery would never use a "Yahoo" or "Hotmail" e-mail address — they would always use a real dot-com domain name after the "@" sign.