security implementation method

[Mark Harris]

Hi

I am new to security and how to implement it. what i would like to do is as
follows
use a database to authenticate users.
if a user is loggeed in only then can they get access to
certian html files in the system.- if they try to go to it directly it
returns access denied or simalar

what would i need to be able to carry out this sort of restriction as these
files are pure html

any help pointing me where to look will be greatly appreciated.

Thanks
Mark