when i download GECK for Fallout New Vegas, i clicked on the exe file, and it sayed that the libvorbisfile.dll file is missing. What should i do??

The NV GECK isnt an installer, you need to extract it into the same folder where FalloutNV is installed. You can make a shortcut of the exe so you can launch it from your desktop.

Yea, you need to place it in "Steam/steamapps/common/fallout new vegas".