Check current sessions and processes

In Oracle how to check current sessions and processes:

set pages 10000 line 200

col username format a15

col machine format a15

col logon_time format a20

col osuser format a10

SELECT NVL(s.username, '(oracle)') AS username,

s.osuser,

s.sid,

s.serial#,

p.spid,

s.lockwait,

s.status,

s.module,

s.machine,

s.program,

TO_CHAR(s.logon_Time,'DD-MON-YYYY HH24:MI:SS') AS logon_time,

s.LAST_CALL_ET

FROM v$session s,

v$process p

WHERE s.paddr = p.addr

AND s.username is not null

ORDER BY s.LAST_CALL_ET, s.logon_Time, s.username, s.osuser;