Ragnars: you need to unpack the .rar file (I don't know what kind of system you are using, but most modern systems will activate some kind of unpacking utility automatically if you click (or double click) on a compressed file.
Once it's unpacked you should have a Landoflegends folder which will contain a .map file. The .map file should be placed in your dominions map directory.
Hopefully that was clear enough.
