As Morqque suggested, you should be able to just place all the files and/or folders provided into the main directory. Typical ENBs are toggled on/off using shift + F12, however, every FH ENB I've encountered starts toggled on when the game is opened.
Sometimes I have this issue, but then realize I've forgotten to switch from OpenGL to Direct3D9 (which is important, because ENB generally doesn't work on OpenGL). If you're uncertain, you can check (and switch) which rendering subsystem you're using in the video section of the settings menu.