With one variable (Numerical or Categorical) you can draw different graphs such as Histogram, Bar Graph, Pie Chart, and Box Plot.
In these Histogram and Box Plot are very useful to draw graphs when the variable is numerical. If the variable is categorical it is better to use bar graph. Any data which can be represented using Pie chart can be plotted using bar graph. Bar graphs are more user friendly than Pie charts.
Watch the video to understand the above explanation with examples.