The exams you can take at an prometric
testing center.
Levels
There are 3 levels of certification. Oracle Certified Associate (OCA)
The associate credential is designed for IT professionals beginning to
work with Oracle.
By earning an OCA certification, you can have increased entry-level job
opportunities.
It is the stepping-stone to starting a successful career as an Oracle
professional.
Oracle Certified Professional (OCP)
The OCP level is intended for experienced people. By earning the OCP
certification you
are on your way to a senior-level position.
Oracle Certified Master (OCM):
The OCM level realy is an advanced level. The exam is difficult and
only few
people are certified.
You need to be able to perform in a real-world, live application
environment in order to pass the test.
Preparation
Before you prepare for these exams you should have knowledge and
experience on the required level for
the field you want to be certified in.
For some certifications you need to follow some training classes
provided by Oracle University.
To prepare often a preparation-book is a good step.
Also test-exams can give good preparation.
for Oracle developers