For OCP certification you have two options, either you can go for Oracle8i or oracle9i systems. OCP certification has three different area of specialization.
1.OCP Database Administrator: for this you have to pass two exams, (1) Orecle9i Database: Fundamentals II and (2) Oracle9i Database: Performance Tuning, 2.OCP Database Operator: for this you have to pass Oracle Internet Database Operator exam. 3.OCP Oracle Developer: for this you have to pass four exams, (1) Introduction to Oracle: SQL and PL/SQL, (2) Develop PL/SQL Program Units, (3) Build Internet Applications I and (4) Build Internet Applications II.
First you have to decide your area of specialization. After that, start with any one of the relative exams.
The study guide alone is enought to pass the exam. Remember, passing the exam and being good at the job are not the same thing. The more you read and the more you "do", the easier you will find Oracle.