Using a .schematic file in minecraft is quite simple. There a few simple steps you need to follow
1. Download MCEdit
2. Launch MCEdit
3. In the meantime download the .schematic file you want to import into your world
4. Open the world you want to import your .schematic file into ( CAUTION! Do not open your world in minecraft and MCEdit at the same time as this may corrupt your world)
5. Click the "import" button
6. Choose the new .schematic file which you just downloaded out of you downloads folder
7. Choose the site you want to place your new download. ( if necessary change the camera angle to an overhead view, i prefer this view over the standard view)
8. Hit enter and then control S to save
9. Open your world in minecraft and enjoy!

Here is a link to my Build Like A Pro Arricle with more on MCEdit. 

http://www.planetminecraft.com/blog/build-like-a-pro/

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Thanks!
Dragon_Hunter_II