OCA or Oracle Certified Associate consists of following Exams. You have to pass these exams to get OCA Certification.
1Z0-001 Introduction to Oracle: SQL and PL/SQL (retired)
1Z0-007Introduction to Oracle9i SQL®
1Z0-047Oracle Database SQL Expert
1Z0-051Oracle Database 11g: SQL Fundamentals
Oracle Database 11g: Administration 1Z0-052
To get training I’d recommend to use SelfTestEngine tool for self preparation or practice exams developed by Exams Expert.