Diagrams prove nothing, but bring outstanding features readily to the eye.
R. A. Fisher ([Fisher, 1925])
Chapter 8 discusses getting an initial overall view of a dataset.
When you first start work on a dataset it is important to learn what variables it includes and what the data are like. There will usually be some initial analysis goals, but it is still necessary to look over the dataset to ensure that you know what you are dealing with. There could be issues of data quality, perhaps missing values and outliers (discussed in the next chapter), and there could just be some surprising basic statistics.
There are several different functions in R for showing what is in a dataset. You can show ...