A huge component of data management and cleaning is summarizing your data. It's hard to know what's really inside data just by looking at it. If you're a frequent user of Microsoft Excel, you might be familiar with creating pivot tables to summarize data and get a feel for what's inside your dataset. We won't use pivot tables with R in this book, but it is possible.
There are various R functions and R packages that allow for the creation of different types of tables to examine data. You can also use the apply family of functions to generate summaries.