X-Camera is packaged as a fat plugin in a zip file. Use your favorite zip utility to extract the contents of the archive into your X-Plane plugin directory. Example:
Note: If you are upgrading X-Camera to a new version make sure you make a backup copy of your X-Camera directory before unzipping the new X-Camera archive. Some unzip utilities can tend to delete the contents of the target directory before unzipping.
There is also a three part series of tutorial videos that will help you get started with X-Camera. You can access them from the X-Camera Tutorial Page.