webMathematica integrates Mathematica with a web server. It builds interactive web sites that carry out dynamic computations and visualizations powered by Mathematica. More information about webMathematica can be found at http://www.wolfram.com/products/webmathematica.
The Wolfram Workbench provides a significant amount of support for webMathematica. This is available in a separate set of plug-ins for the Workbench. You can learn about this from http://www.wolfram.com/products/workbench/webmathematica.html.