PostgreSQL System Views or Dictionary Tables

Hello,

I'm new at PostgreSQL, but known Oracle since ten years ago.

In PostgreSQL, where can i found system views or dictionary tables (v$*, dba_* at oracle) or structural dba tables ?. And comand prompt parameters of the database (show param X at Oracle) ?
The porpose of this is to familiarized with the structure of Postgresql databases.

My test environment: Windows physical server machine intel x86-64 architecture with PostgreSQL Database version 10.5 and pgAdmin 4 version 3.2 .

Thanks so much for your help.
Regards,
Diego.