Sometimes, you need to see a list of all the tables in the database. In Oracle, you can query the data dictionary to see this.
There are several views in the data dictionary you can query, and which ones you can see will depend on your privileges. The easiest way to see all tables in the database is to query the all_tables view:
SELECT owner, table_name FROM all_tables;
This will show the owner (the user) and the name of the table. You don't need any special privileges to see this view, but it only shows tables that are accessible to you.
If you have administrator privileges, you can query the dba_tables view, which gives you a list of all tables in the database.