I created a new item in purchase item master. now I am trying to create a requisition and purchase order but that item is not displaying in find dialog box.
is I have to submit for approval? if yes please guide me how to submit for approval.
It is not enough, if you just create an item.
It needs to be enabled for purchasing and available in the master org (inventory organization that is configured as item validating org in the Purchasing --> Financial options menu).
If you are new to apps, the best thing is to use copy item menu to create a new item or use the purchasing template to create new items.
Else, you can use, one time items (i.e only provide item descriptions in the req\po along with category) and create req\po.