Explain when and why a Bar Graph is appropriate for describing the data.

I need some help answering these questions:
1). Explain when and why a histogram is appropriate for describing the data.
2). Explain when and why a Bar Graph is appropriate for describing the data.
3). What particular elements of the graph do you want the reader to notice when viewing a histogram?
4). What is the overall impression that you expect the reader to have from looking at the graph?
5). What particular elements of the graph do you want the reader to notice when viewing a Bar Graph?
6). What is the overall impression that you expect the reader to have from looking at the Bar Graph?