With most web hosts you’ll find lists of the various web server technologies available as included or optional software; the importance of these depends on what you’re hoping to do with your site, and how it’s built. Beginners can probably make do with no extras at all, but life will be easier if the host offers pre-built CGI scripts, allowing you to add features like email forms to your pages with the minimum of effort. The best packages provide full CGI support, meaning you can add your own scripts (the most flexible solution).
If you’ve built your site with Microsoft FrontPage, and made use of the advanced tools like the Site Search gizmo, then you’ll also need to make sure your host offers support for the FrontPage server extensions. Server-side scripting via ASP (Active Server Pages) is another Microsoft feature worth having, if only to give you flexibility in the future.
To provide a small database on your site (eg a searchable directory), look for key words like ‘Access support’ or ‘ODBC’. A complex database, or one that will be accessed by many people, may require something like ‘mySQL’ or ‘SQL Server’, but you need to discuss this with whomever will be creating or maintaining it.
There are plenty of more specialized extras, like SSL (secure server space, perhaps for taking credit card numbers), or RealAudio support (for streaming media), but unless they’re essential to you, don’t worry about them initially. Many hosts are very flexible, and are able to add features to a package for a small additional cost.