PostgreSQL, often simply Postgres, is an object-relational database (ORDBMS) – i.e. a RDBMS, with additional (optional use) "object" features – with an emphasis on extensibility and standards compliance. As a database server, its primary function is to store data securely, and to allow for retrieval at the request of other software applications. It can handle workloads ranging from small single-machine applications to large Internet-facing applications (or for data warehousing) with many concurrent users; on macOS, PostgreSQL is the default database – for web hosting – and it is also available for Microsoft Windows and Linux (supplied in most distributions). PostgreSQL is ACID-compliant and transactional. PostgreSQL has updatable views and materialized views, triggers, foreign keys; supports functions and stored procedures, and other expandability. PostgreSQL is developed by the PostgreSQL Global Development Group, a diverse group of many companies and individual contributors. It is free and open-source software, released under the terms of the PostgreSQL License, a permissive free-software license.
PostgreSQL manages concurrency through a system known as multiversion concurrency control (MVCC), which gives each transaction a "snapshot" of the database, allowing changes to be made without being visible to other transactions until the changes are committed. This largely eliminates the need for read locks, and ensures the database maintains the ACID (atomicity, consistency, isolation, durability) principles in an efficient manner. PostgreSQL offers three levels of transaction isolation: Read Committed, Repeatable Read and Serializable. Because PostgreSQL is immune to dirty reads, requesting a Read Uncommitted transaction isolation level provides read committed instead. PostgreSQL supports full serializability via the serializable snapshot isolation (SSI) technique..
This video contains basic commands to:
CREATE DATABASE,    CREATE SCHEMA,    CREATE TABLE,
DROP DATABASE,    DROP SCHEMA,    DROP TABLE,
VIEW TABLES,    INSERT VALUES INTO TABLES,    SELECT FROM TABLES.