If you want to use a script, you have to source it first. Open the script editor and goto file source script. Look for the script you want and source it.
Before you use any script you should open it in a text editor. Sometimes the mel script has info telling you how to use it.
After this is done in the command promt type the name of the script and any settings required. For the spiral mel, try typing spiral 10 1 5 .This will create a spiral curve that is 10 units high, 1 unit in radius and makes 5 loops.
Hope this helps.