There are three ways to get started, they are: formal training, self training and on-the-job training.
1) Formal training, you know what I mean.
2) Go to http://www.oracle.com, download Oracle sofware, install it and start practicing e.g. build your own lab. Oracle documentation is pretty clear and, it's for free!
3) Find a job in a SQL Server / Oracle shop and ask your new boss to involve you in Oracle.
Godspeed!
_____________________________________
Pablo (Paul) Berzukov
Author of Understanding Database Administration available at Amazon and other bookstores.
Disclaimer: Advice is provided to the best of my knowledge but no implicit or explicit warranties are provided. Since the advisor explicitly encourages testing any and all suggestions on a test non-production environment advisor should not held liable or responsible for any actions taken based on the given advice.