So I just downloaded and instelled SQL Workbench/J as my it department said, to help me with sql queries. they also told me "Download a JDBC driver that will enable SQL Workbench/J to connect to your cluster. Currently we recommends this version 8 JDBC driver: http://jdbc.postgresql.org/download/postgresql-8.4-703.jdbc4.jar
I did it but I am not an expert, therefore I supposed I had to install it. Am I wrong?
No, you are not wrong. You will need the jar file for SQL Workbench/J.