Create a new requisition
Go to Navigation pane > Modules > Procurement and sourcing > Purchase requisitions > Purchase requisitions prepared by me.
Select New.
In the Name field, give the requisition a name.
In the Requested date field, enter a date.
In the Accounting date field, enter a date. Select OK.
In the Reason field, select an option from the drop-down menu. Select the reason.
In the details field enter a more descriptive justification for the requisition.
Add a line to the requisition
Select Add line. There are two ways of adding lines to the purchase requisition. If you already know the product number or you already know that you are requesting a product that is not in the product catalog, then you can add the line directly with Add line. The other way is to use Add products where you can use searching and filtering to find items in the product catalog.
Select the row you just created.
In the Item number field, type a value. The items that are available for you to choose are limited by the category access policy and the procurement catalog for the buying legal entity.
In the Quantity field, enter a number.
Submit the requisition
Select Workflow to open the drop dialog.
Select Submit.
Close the page.
In the Comment field, type a note for the approver of the requisition.
Select Submit.
Close the page.
Refresh the page.
Reference:
https://docs.microsoft.com/en-us/dynamics365/supply-chain/procurement/tasks/create-requisition-consumption

Reference:
https://docs.microsoft.com/en-us/dynamics365/supply-chain/master-planning/planning-optimization/get-started