After unpacking this file, you can place the F/A-18C HORNET pit V*.* map into the saved games folder.
...users/[name]/saved games/DCS.openbeta/Liveries/Cockpit_F-18C
If after unpacking the files are not in a folder, please make one in the above mentioned path, and place the files in that folder.
Then in DCS, go to options (settings), select the SPECIAL tab, select F/A-18C and in customized Cockpit select FA-18C HORNET pit V1.8.