A password generator creates a unique password for each web site you use. To use it, you go to the password generator page, and enter your master password, and the URL of the web site. The password generator combines these, usually using a hash algorithm, producing a unique password for the site.
While password generators are a good idea, they are inconvenient to use, so most people continue to use the same password on all web sites. Some password makers have browser extensions to make them more convenient. However, single sign-on, e.g. OpenID seems to be a more promising approach to the problem.
Some password generator sites:
The idea of a self-decrypting page (SDP) is that it's a self-contained HTML page, that requires a password to view it, but does not require the reader to have any special software installed.