Question: what are the cube notations?
Answer: A single letter by itself refers to a clockwise face rotation in 90 degrees (quarter turn): FRULBD. A letter followed by an apostrophe means to turn that face counterclockwise 90 degrees: F'R'U'L'B'D' A letter with the number 2 after it marks a double turn (180 degrees): ...  An example algorithm R U R' U R U2 R' U.