When running a reliability analysis (using Cronbach's alpha) in SPSS, what does "scale" refer to? Do I have to compute a scale explicitly beforehand?

Is the scale meant to represent the sum of responses (each response is an element of, say, the set {1, 2, 3, 4, 5}) of a case (an individual) to a set of questions (items)? And is a "scale mean" the mean of the values of the scale variable in the entire sample?