It's trying to tell you that you are supposed to give the script a parameter, which it calls site_code.
I don't know what lcdmetar.pl is or does but it's saying you should invoke it something like this:
You'll need to check out some documentation for the product to see what it expects you to pass it as site_code.
A quick google has thrown up a copy of lcdmetar.pl, and site_code seems to be a code for your geographical region so it can look up your local weather. You'll need to look up the documentation to work out the correct site code for your part of the world and then pass that code as a parameter.
Try passing it EGLL (which is London Heathrow Airport):
More codes can be got from here:
Must go get the dinner on now!