1. Go to the web page that uses Java. Really any web page that uses Java will do. If you just want to test it out, you can go to
2. You should get a popup asking if you want to install Java. Go ahead and say yes. This will install the Java runtime on your system and make it available for standalone apps and your web browser plugins. The steps after this one are required to enable Java for browser plugins and Web Start apps.
3. You will now need to run an application called "Java Preferences." A quick Spotlight search should bring it right up.
4. Click on the "General" tab if it is not already selected and then check the "Enable applet plug-in and Web Start Applications" box.
5. In my case, this was a Web Start application I needed to run so I also had to go into the System Preferences and allow all applications to run. This can be found in "Security and Privacy" area then "General" tab and then "Allow applications downloaded from" needs to have the "Anywhere" button selected to allow Java Web Start applications that have not been signed with a developer certificate.
I hope this info is helpful as I spent a bit of time tracking down all the required steps and wondering why things weren't working.
* I know it's old news, I'm still not used to it.