To enable "Chart Trading" click the mouse icon on the top right corner of the chart. Once you enable it you should see a little font appear on the lower left corner of the chart that reads "Hold CTRL key to place more orders". To place an order is simple, simply hover your mouse cursor at a specific price level and you will notice two order types will be displayed. The order types available are determined based on the price level your mouse cursor is located.
To place the order all you need to do is either left click or right click. Left click will execute the order located on the left, right click will execute the order located on the right.