Because continuous data is much more common outside of political science/international rela­tions (IR), there are a wealth of resources for further reading.

Marchant-Shapiro, T. (2015) Statistics for Political Analysis: Understanding the Numbers. London: Sage/CQ Press.
This book includes some basic instructions for using SPSS to conduct data analysis, and the examples are from political science. See chapter 3 (‘Measures of central tendency: That’s some mean baseball’) and chapter 4 (‘Measures of dispersion: Missing the mark’) for further read­ing on descriptive statistics for continuous variables. See chapter 10 (‘Measures of association: Making connections’) for correlation and Pearson’s r.

Pallant, J. (2016) SPSS Survival Manual. Maidenhead: Open University Press/McGraw-Hill Education.
This book provides a functional overview of how to produce statistics in SPSS. See chapter 6 (‘Descriptive statistics’) for measures of central tendency and dispersion. See chapter 11 (‘Correlation’) for an overview of correlation and Pearson’s r.

Urdan, T.C. (2017) Statistics in Plain English, 4th edn. Abingdon: Routledge.
This book discusses statistical concepts in much more accessible language than most. See espe­cially chapter 2 (‘Measures of central tendency’) and chapter 3 (‘Measures of variability’) for further reading on descriptive statistics for continuous variables. See chapter 12 (‘Correlation’) for further discussion of correlation and Pearson’s r.