If you're new to charting and graphing, this page is a brief description of charts, the benefits of using Javascript charts and some descriptions of the commonest chart types.
A graph (or chart to use the correct term - a graph in computer science is something else) is simply a graphical representation of your data. This representation will be easier to understand than a long list of numbers and far more illustrative (of trends for example). The actual data is represented by different symbols depending on the chart type - bars in a Bar chart, lines in a Line chart and slices in a Pie chart. Different chart types can represent different sets of data better. For example a Line chart can be used to represent chonological data quite well and a Pie chart might be better at representing percentages.
Javascript charts are charts which are made using browser based Javascript. New HTML5 features allow far easier creation of charts, such as the HTML5 canvas tag. Charts made in this way (ie in the users browser) are often faster than their server based counterparts and can be used as a way of reducing bandwidth/load/stress on your server. They can therefore be used to prolong the life of your hardware, at the same time as improving the resposiveness of your website.
RGraph is a Javascript charts library that makes it far easier to produce these charts (roughly 20 different types). It uses the HTML5 canvas tag in conjunction with Javascript to draw the charts.
A Bar chart represents data with one bar, or segment of a bar, for each piece of data. There's an example of a Bar chart on the right. The RGraph Bar chart can be grouped or stacked, and the X axis can be either at the bottom, center or the top.
You can see the full range of bar chart options on the Bar chart documentation page.
A Line chart represents data through a series of points, connected by a line. There's an example of a Line chart to the right. You can have multiple lines on the chart, it can be filled, stepped or ranged. Like the Bar chart, the X axis can either at the bottom, center or the top.
You can see the full range of line chart options on the Line chart documentation page.
A Pie chart represents data as segments of circle. As such, it can be good at showing things such as precentages. Bear in mind though that it has been criticized as not being the easiest way to compare individual sections. More information is available on the Wikipedia page.
You can see the full range of Pie chart options on the Pie chart documentation page.
RGraph supports roughly 20 different types of chart in total. Besides the Bar, Line and Pie there is: Bipolar, Donut, Funnel, Gantt, Horizontal Bar, Horizontal Progress Bar, LED display, Meter, Odometer, Radar, Radial Scatter, Rose, Scatter, Thermometer, Vertical Progress Bar and Waterfall chart. For more information on each chart type you can read the appropriate chart types documentation page. Besides the individual chart documentation pages you can also read about the many features of RGraph.