Hi Yogi Yang,
Psql is a very strong tool, and easy to use. Please find the answers for your queries
>>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
postgres=#\d{t|i|s|v|S|g|n}
you can use any of the things as per your requirement
>>4. Retrieve list of all Login Roles
>>5. Structure of a Table
postgres=# \d <tablename>
Hope this will help you out
Regards
Raghavendar