thx!
30 mins later, i did set it up as how i want it!!!
For the people who will search for this:
Enable SNMP first:
set snmp name SRX_name
set snmp community XXXXX authorization read-write
set snmp community XXXXX clients 192.168.0.0/18 --> set up the addresses
set interfaces xxxxx traps
Then i search for the Mib you want like in : http://www.juniper.net/techpubs/en_US/junos12.3/topics/reference/mibs/mib-jnx-if-extensions.txt
then the next step would be, in this case for packet rate for interface fe-0/0/6.0 :
serdar@SRX210# run show snmp mib walk ascii ifIn1SecPkts
............ifIn1SecPkts.536 = 0
ifIn1SecPkts.537 = 5811
ifIn1SecPkts.538 = 0
serdar@SRX210# run show snmp mib walk 1 | match fe-0/0/6
ifDescr.515 = fe-0/0/6
ifDescr.537 = fe-0/0/6.0
serdar@SRX210# run show snmp mib walk ifIn1SecPkts | display xml | match 537
<name>ifIn1SecPkts.537</name>
<index-value>537</index-value>
<oid>1.3.6.1.4.1.2636.3.3.1.1.3.537</oid>
[edit]
serdar@SRX210# run show snmp mib walk ifOut1SecPkts | display xml | match 537
<name>ifOut1SecPkts.537</name>
<index-value>537</index-value>
<oid>1.3.6.1.4.1.2636.3.3.1.1.6.537</oid>