A data table is a list of statistics - a graph is a physical representation of the data.
if you dont know ask your math teacher
The earliest known pie chart is generally credited to William Playfair's Statistical Breviary of 1801, where two such graphs are used according to WikiPedia Some sources say Florence Nightingale invented the Pie Chart in 1857, but in fact even the Florence Nightingale museum admits she did not. She was an amazing person, but unfortunately not the inventor of the pie chart.
They are used for when each data group contains two different sets of frequency data. A double bar graph is used to compare both between and within data groups
You can use a bar graph when you are working with numers. :)