Understanding the architecture of a running Oracle database instance is one of the key differentiators between an outstanding DBA and a run-of-the-mill DBA. Learn the architecture well. I'm always surprised at how many people don't do this. Knowledge and understanding of how Oracle works behind the scenes is critical to the tuning process. It can also be very helpful when it comes to planning for backup and recovery. If you learn the architecture well, you will be able to solve problems that other people can't, and you will be well on your way to certification and a successful career as a DBA.