Data tables and graphs are just representations of abstract ideas. For example, if a business wants to review sales for the year 2010, it is easier to look at a chart that has grouped the data, or a graph that shows if the sales activity went up, went down, or stayed about the same.
Drawing conclusions on graphs and data tables does require a little bit of knowledge. If it is a graph, what are the labels for the x and y axes? This may help you understand what the graph represents.
Also, if there is additional information, it may be listed in a 'legend' or an appendix to the data table.