Installation is rather a misnomer for Selenium. Selenium has set of libraries available in the programming language of your choice. You could download them from downloads page
Once you’ve chosen a language to work with, you simply need to:
The Selenium RC server is simply a Java jar file (selenium-server-standalone-<version-number>.jar), which doesn’t require any special installation. Just downloading the zip file and extracting the server in the desired directory is sufficient.
Before starting any tests you must start the server. Go to the directory where Selenium RC’s server is located and run the following from a command-line console.
java -jar selenium-server-standalone-<version-number>.jar
This can be simplified by creating a batch or shell executable file (.bat on Windows and .sh on Linux) containing the command above. Then make a shortcut to that executable on your desktop and simply double-click the icon to start the server.
For the server to run you’ll need Java installed and the PATH environment variable correctly configured to run it from the console. You can check that you have Java correctly installed by running the following on a console.
java -version
If you get a version number (which needs to be 1.5 or later), you’re ready to start using Selenium RC.
For details on Java test project configuration, see the Appendix sections Configuring Selenium RC With Eclipse and Configuring Selenium RC With Intellij