Blue Prints

If you download a blueprint, you have to place it in the "Blueprints" folder in your game directory (if it does not exist, just create it). Do not extract the blueprint file, unless it's stored in a zip archive (some zip programs recognize the .blueprint file as a zip archive, unzipping it breaks the file).
Then start the game, and open your journal. Now you should be able to see the new blueprint in the "Blueprints" section.

In order to place it in the world, you have to craft a "blueprint" item at the workbench, hold it in your hands, select the desired blueprint in the journal and hit the "Use" label