What is FrontPage and what is a Frontpage Extension
FrontPage is Microsoft's web design program, a powerful environment for creating, editing, and publishing web pages. Its user-friendly interface allows you to create professional page elements like buttons, forms, counters, etc., without bothering yourself with the HTML code behind the scenes.
FrontPage uses its own internal language and tools to transform your user-friendly actions into an end-product that can be served on the Internet. In order to generate this end-product, FrontPage needs to run on a machine that supports its internal language. On your local machine, this support comes with FrontPage itself.
The problems may begin when you upload your site to a remote server.
Hosting servers rarely have FrontPage itself installed, but if you want to run your FrontPage-generated site on them, they must speak FrontPage's language. This feature can be separately installed, and is known as "FrontPage extensions".
If you plan to build your site on FrontPage, look for a hosting provider that guarantees a full installation of FrontPage extensions. Otherwise, pages that run smoothly on your local machine may surprise you with errors or unpredictable behavior as soon as you upload them.
If you already have a hosting plan that doesn't offer FrontPage extensions, you will need to either forfeit most of FrontPage's functionality and stick with its most basic features, or switch to another web design software.