Hover over the plugin. You will see some text appear to the right side. One will be 'Install". This will add it to your active plugins list. Some plugins have configuration options; once they are installed. Again; hover over the installed plugin, if "Settings" appears to the right, there are configuration settings for that plugin.
Yes. 1.8.1 build 10200 is correct. To install the plugin all you should have to do is hover over it with your mouse. You should see "Install" "Delete" to the right of the plugin. Click on "Install". It should then install, and move to your installed plugins page. If you don't see this, something else is wrong, and Ross will need to jump in.