Hello dipak,
/SAPTRX/EH_HDR : this is populated just when you create your freight order
/SAPTRX/EH_EVMSG: this is populated when an event is reported against your event handler I.e your FO
/SAPTRX/EVM_HDR: this is populated at the same time when an event is reported.
The difference is that 3rd table contains hdr details of the event message received but the 2nd table has a EH_GUID relationship with the EH_HDR table.
Hope this helps. Please let me know in case off any further questions.
Thanks,
Deb