Opatch is a tool for applying one-off-patches for oracle-products, that means if you are running in bug xy the the support will tell you to apply the patch 08154711...
In my case a found a metalink-note that could solve my problem, guess what... YES i had to apply a patch... It took me a lot of time to find the download-page for opatch. The note described exactly what opatch is doing, referred to a lot of other notes....
So here is the shortcut directly to the opatch-download-page:
http://updates.oracle.com/download/2617419.html
By the way, you need an valid metalink-account for that link