1.) Download the game (I know you already done that.)
2.) Right-click on the file and click extract file then wait.
3.) Go into the folder which is called DDLC.
4.) There should be a DDLC.exe file so you click on it.
5.) Agree that you're over 13 years old and that you don't have any mental health problems.
6.) Enjoy yourself.
If this doesn't work try re-downloading the game and following these steps once again.
Love from Amelia x