Where to start
Where to start: My recommendation is to start with PostgreSQL an open-source database. You can find it at:https://www.postgresql.org/ I can only say that my beginnings in learning databases were with PostgreSQL, and when I was studying, our college professor insisted on this database.
First thing that you need to do is to type in search bar PostgreSQL or just follow this link PostgreSQL Home page
On the page, click on the Download section and choose your operating system.
Example of a connection on localhost PostgreSQL database.
Oracle Database Hints