Before you can use Reactor you need to download it and configure it on your server.
Reactor is available for download in two places. A zip file of Reactor can be downloaded from DougHughes.net at http://www.doughughes.net/includes/reactor/reactor.zip. This zip file tends to be a stable release, but is also significantly out of date.
The zip file contains these folders:
/Reactor The Reactor core files.
/ReactorSamples Sample applications demonstrating Reactor.
/Documentation This documentation.
You can also download Reactor from the public Subversion repository.
Note: The public subversion repository contains development code. It may be badly broken at times or the API may change before the next Zip is released. That said, its really the best location to get the best code. As the project progresses you can watched for tagged milestones instead of using the bleeding edge version.
To get the code from Subversion, use your favorite Subversion client (I like TortoiseSVN - http://tortoisesvn.tigris.org) and point it at: http://svn.reactorframework.com/reactor.
The trunk folder is where the latest and most bleeding edge release can be found. The branches folder holds various branches of Reactor (none as of this writing) and the tags directory holds specific stable milestones (none as of this writing).
In the Trunk folder there are several folders. You will be most interested in:
/Reactor The Reactor core files.
/ReactorSamples Sample applications demonstrating Reactor.
/Documentation This documentation.
The rest of the folders can be disregarded.