Hi,
here is a certification path for PL/SQL Developer:
link
OCA - means "Oracle Certified Associate", this is an entry level certificate
OCP - "Oracle Certified Proffesional", this is higher level than OCA
OCM - "Oracle Certified Master", this is the highest level
To get OCM you must be OCP, to get OCP - you must first get OCA.
To get OCA PL/SQL, you must pass one of the PL/SQL exam from these two: 1Z0-147 (older exam, based on Oracle 9i) or 1Z0-144 (newer exam, based on 11g),
and additionally one of the SQL exam from these three: 1Z0-007, 1Z0-051 or 1Z0-047
1Z0-007 and 1Z0-051 can be passed online (you can take it from home) and cost 125 USD,
1Z0-047 is a proctored exam (you must take it in the Certification Center), costs more ~200 USD and is tighter than 1z0-007 and 1z0-051,
but it gives you an additional certificate - Oracle SQL Expert.