On the mobile device you may create a purchase order. That is at Dashboard > Buy

Dashboard > Buy

Type quantity > Finish 

Save

If you touch the amount you may change the quanitity or the cost of the item 

Edit quantity or cost > Finish 

Touch the icon to receive the items into the inventory

On the web version you may create the purchase order for your supplier. That is at Main menu > Purchase orders > +

Main menu > Purchase Orders

Purchase > Plus sign 

Type the quantity and then Save & Continue (You may select a category o the Supplier)

Click on Finish

Now on web you may add the shiiping date, cost andf notes on the purchse order

Select the purchase order just made 

Click on the receive icon to enter the quantity into the inventory

Remarks: when your license is Multi-Wearhouse select the whearhouse where you are going to receive the items from your supplier.