For using the schematic you need a program called MCEDIT once this is downloaded you can place the mansion in your world by downloading the schematic file and placing it somewhere you can locate, (once you load mcedit you should get a schematics folder) Then Open up MCEDIT and click open world then select your world (Windows;%appdata%,roaming,minecraft,saves,nameofworld,level.dat) (Mac;Library,Application Support,MInecraft,saves,level.dat)
Then it will open in this editor where you can click import schematic and you can navigate towards where you placed it.
Now place the schematic which should be inside a green box somewhere you want it, it might take a few times to get this right.

If I haven't explained it very well use this link,
http://www.mcschematics.com/index.php?topic=13649.0