Add the class .chart-holder
to your div that is going to contain the chart. This helper class give the chart container a default height which it needs to display properly.
<div id="bar-chart" class="chart-holder"></div>
You can find chart examples for line, pie, donut, vertical bar and horizontal bar charts in the /js/demos/charts/
folder. The code is clean and organized and should be a great start in creating your own charts.