When you right click, the wording will depend on your internet browser, but will be 'Save link as...' in Firefox.
Alternatively, if you click and see the text file (which is actually the chart, encoded in a text based format, with a header like this:
"! 2011 imgkap 1.11 - at 02/12/2013 from SimpleEstuary.tif"), then you can just save the file, making sure you use the extension .kap
If you then put the chart file in the folder where OpenCPN is expecting to find the charts, you should see it in OpenCPN. You may have to select the correct chart/zoom level in order to see it. The 'real world' location used for this training chart is south of Ireland, and west of Cornwall (SW England), so you may well see a blank base map until you manually select the correct chart in OpenCPN.
I hope this helps, please let me know if you need any more guidance.