How to retrive List of Tables in a Database using...

Hello,

I am new to pgSQL. I would like to know if there is a way to do the
following using pure SQL:
1. Retrieve list of all Tables in a database
2. Retrieve list of all Functions, Triggers, Sequences, Views, etc.
3. Retrieve list of all Group Roles
4. Retrieve list of all Login Roles
5. Structure of a Table

TIA

Yogi Yang