Oracle have provided a whole range of pre-built VirtualBox images which make it incredibly easy to get to grips with their products straight away.
for example say you wanted to try using Oracle11gR2 on Linux, you could create a Linux host, build it, configure it and then install all the software...
or you could just download the image and import it into VirtualBox.
and of course once you've modified the image you can take snapshots so that you can return to what you were working on or you could load the original image and start again.
These are created for Oracle Developer Days and as well as the products you'll find a handy lesson guide as well so that you can follow the same lessons at home.
The only thing that will be missing is the coffee, sandwiches and a chat in the Oracle office!