The Angel Game (Also known as the Ouija board or Kokkuri-san/Prophesy-san) is an activite that you call on a certain object, and get the answers to questions depending on how the object moves.
As explained by Yuuko in the manga. You take on a large paper and write out fifty symbols specifically: Numbers, Letters, etc. then you touch a pencil or a 10-yen coin to the paper.
It is also said that people call it th angel game (despite the fact having other names) because Angel sounds softer. And it is said that the angel game is a very dangerous activite by Yuuko