There are several PostgreSQL extensions preinstalled, that you can enable for your cluster. You can enable the extension by logging into your cluster and executing:
create extension <EXTENSION> CASCADE;
The following table shows which extensions are enabled by default and which can be enabled (PostgreSQL version 12):
select * from pg_available_extensions;you will see more available extensions, but many of them can't be enabled or used without superuser rights and thus aren't listed here.