Hi Dinesh,
OPPQ is nothing but shortcut key or hotkey to reach the mrp customization. you can see the same in spro > production > material req planning.
you can see the transaction code in menu bar > additional information > display key > documents (where last four char is the transaction code)
for alternate transaction codes - please do search it sdn, you will get all the answers.
hope this helps.
regards,
Solomon