DBA_USERS describes all users of the database. DBA_AUDIT_SESSION displays all audit trail records concerning CONNECT and DISCONNECT. So the following query might help undretstand and Track user login:
SELECT s.username,
s.userhost,
s.terminal,
s.timestamp,
s.action_name,
u.*
FROM dba_users u LEFT JOIN dba_audit_session s ON u.username = s.username
WHERE u.account_status = 'LOCKED';