Calculating Mean for multiple variables into new single variable in SPSS Questionnaire analysis

Calculating Mean for multiple variables into new single variable in SPSS
(Mean function)
Compute variable
(Questionnaire analysis)
(Likert scale)

[@anisalshargabi1244]

Thank you Prof. suppose we have 3 main variables (independent variable), (dependent Variable) and (Mediating variable). each variable is measured by some already established and validated scale. and each scale has about 4 Dimensions with about 3 statements for each dimension. and all items were scored on a 7-point Likert scale 1=Strongly Disagree to 7=Strongly Agree. How would be the correct analysis process for each dimension and each scale? and how would be the correlation analysis between the 3 variables? and for the total scores of dimensions/scales, should we use averages (means) or sums and why?. thank you very much in advanced for your kind clarification.