Sampling is at the very core of statistical tests: drawing conclusions on research populations based on (small) samples from those populations. Basically all statistical tests quietly assume that the data you're analyzing are a simple random sample from your population. This assumption being ignored is the very reason why political polls are often widely off and research findings can't be replicated.
The tutorials below explain what sampling is and how to draw random samples from your data in SPSS. Mastering this skill greatly facilitates running simulation studies like we presented when explaining ANOVA and the chi-square independence test.