USER_SOURCE describes the text source of the stored objects owned by the current user. This view does not display the OWNER column.

select * from user_source where type='TRIGGER' and lower(text) like '%order%' 

ALL_SOURCE describes the text source of the stored objects accessible to the current user.

select * from all_source where owner=:owner

DBA_SOURCE describes the text source of all stored objects in the database.

select * from dba_source

select owner, table_name
from all_tables

ALL_TAB_COLUMNS describes the columns of the tables, views, and clusters accessible to the current user. COLS is a synonym for USER_TAB_COLUMNS.

select *
from all_tab_columns
where table_name = :tname

All roles granted to user.

select * 
from dba_role_privs 
where grantee= :username

Privileges granted to user:

1. system privileges

select * 
from dba_sys_privs 
where grantee = :username

1. object grants

select * 
from dba_tab_privs 
where grantee = :username

Permissions granted to roles.

Roles granted to other roles.

select * 
from role_role_privs 
where role in (select granted_role from dba_role_privs where grantee= :username)

1. system privileges

select * 
from role_sys_privs  
where role in (select granted_role from dba_role_privs where grantee= :username)

1. object grants

select * 
from role_tab_privs  
where role in (select granted_role from dba_role_privs where grantee= :username)

select * 
from dba_objects

Remarks

The data dictionary views, also known as catalog views, let you monitor the state of the database in real time:

The views prefixed with USER_, ALL_, and DBA_, show information about schema objects that are owned by you (USER_), accessible by you (ALL_) or accessible by a user with SYSDBA privilege (DBA_). For example, the view ALL_TABLES shows all tables that you have privileges on.

The V$ views show performance-related information.

The _PRIVS views show privilege information for different combinations of users, roles, and objects.

Oracle documentation: Catalog Views / Data Dictionary Views (opens new window)