If you are talking about Secured HTML (SHTML files, the ones that make your browser address bar go green) then the first thing you need is a security certificate - which you have to pay for. You are looking at around £200 pa to £thousands pa depending on your need. Look at the biggies: Verisign
], and so forth - Gooogle can help you there.
There is more info here: What is SSL and what are Certificates