a half day i've finished it with 3 other friends

now you see a tab with all kinds of information (amount of views, download amount etc.) above that, you see "MCEdit schemetics" after you've clicked it, save the file.
After that you'll open a programm that supports MCEdit schemetics, preferably MCEdit (http://www.minecraftforum.net/viewtopic.php?f=1022&t=15522&sid=ba49cdea4c06038ea84aead559b3dd0e download link is underneath the tutorial vids)

Run MCEdit and import (by clicking "open a level") the schematics you've downloaded.
the Huge Castle should now appear in MCEdit.

press save (name it Huge Castle or som'thn) and close mcedit, open minecraft, do singleplayer and select "Huge Castle"

Hope it helped