The focus of this class in not statistics or mathematics but political science. We will not reproduce statistics using complex formulae, but instead use statistical software to generate statistics and graphs from real data sets that are substantively interesting to social scientists. Collections of data are typically described as data sets. Data sets generally have a rectangular structure.
Data sets are a matrix of rows and columns.
If you are a familiar with a spreadsheet, then you are familiar with the layout of a data set. Columns are variables.