By "all" tables you mean regardless of owner? The dba_tables is what you need to query. If less than 100%, then variations of #1 below (restricted by owner for dba_ and all_) can be used.

1) select table_name from dba/all/user_tables

A quickie query for a user is:
2) select * from tab;

("TAB is included for compatibility with Oracle version 5. Oracle Corporation recommends that you do not use this view.")