To use it, you just give the cleartext HTML file as stdin and get the encrypted HTML file as stdout. The decryption passphrase is given as a command-line argument. Then send out only the encrypted HTML file, and tell your readers the passphrase. Without the passphrase, the file is not readable; with it, the file decrypts and displays itself.
You could distribute the encrypted HTML file via a web site, a CD- ROM/DVD, email, whatever. Since it doesn't depend on a web server for security, any transmission method will work.
See the manual entry for more details.
Here's an example - the <iframe> to the right contains a page encrypted by this program. The passphrase is xyzzy. Go ahead and try it.
ACME Labs / Software / SecurePage