There's a whole world of cubing, with websites and YouTube channels and speedsolving competitions. All the way back in the early 80s there was a newsletter, and that's where the standard notation was first published, by David Singmaster. The faces are lettered based on their orientation with respect to the person holding the cube: the one facing the cuber is F for Front, the one facing away from them is B for back, the one to their left is Left and the one to their right is Right. Now, the other two faces would be Top and Bottom, but that would introduce a collision on the letter B, so Singmaster instead uses U for Up and D for Down.
A letter by itself indicates that you should rotate that face a quarter turn clockwise. A letter with a prime/apostrophe, like R', means you rotate it counter-clockwise, and would naturally map to the shifted face letter on the keyboard. A letter followed by the number 2 indicates a 180º rotation, and it of course doesn't matter whether you do it clockwise or counter-clockwise.
The middle slices names are less obvious but fairly mnemonic. The horizontal slice between U and B is E for Equator, and "clockwise" is reckoned looking down through the Up face; the vertical slice between L and R is M for Middle, and clockwise is reckoned looking through the Left face; and the other vertical slice between F and B is called S for Standing, and clockwise is reckoned looking through the Front face.
For whole cube rotations, you use axis notation: the X axis runs between L and R, the Y axis between U and D, and the Z axes between F and B, and the name of the axis means to rotate the whole cube 90º around it. Direction around Y is the same as E, and direction around Z is the same as S, but perhaps confusingly, rotation around X is reckoned the opposite way it is for M, with X denoting a clockwise rotation as seen through R. This is consistent with the right-hand rule for algebraic axes, though; in each case you reckon clockwise by looking from the positive direction along the axis back toward the origin (which is at the center of the cube).