Selenium Core is one of several ways you can use Selenium for browser automation. One of the easiest ways to get started is to use "Selenium IDE" to record a test and play it back. (At the time of this writing, May 2006, Selenium IDE only works in Firefox.)
http://wiki.javascud.org/display/SEL/Getting+Started+with+Selenium+Core
http://wiki.javascud.org/display/SEL/Selenium+Core+-+Wiki
http://wiki.javascud.org/display/SEL/Selenium+chinese+translation+road+map