Hello Mohmmad,
if you want to know how many people are in the low, medium or high PSS groups, I'd recommend using "Recode into Different Variables" to recode the PSS_sum_score into a new variable, PSS_level, say, and then using the Frequency command on that.
Running Frequencies on PSS_sum_score itself will just tell you the frequency of 0s, 1s, 2s, etc, as is seen in the output you shared - the value labels are purely labels and don't change how SPSS treats the data.
I'm not sure why you'd want to calculate means and SDs of PSS in the three groups, but if you really want to do that you could use your new PSS_level variable as a grouping variable when asking for means and SDs of your PSS_sum_score.
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Tom Goodale
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