The values they act on are arguments, and generally have to be defined by the user. You can think of arguments as pointers, telling the keyword where it's supposed to go before it performs its assigned task.
In the example image above, I've used a gotoAndPlay() command. In this case the command is gotoAndPlay(19); in this case, the number 19 is the argument. It tells the command which frame it's supposed to reach before it plays. The requirements of arguments for each command are usually quite specific; each command has pre-defined values that it requires to operate. You couldn't put the word "earbuds" in the place where the frame number should go in the gotoAndPlay() command.