The Purchase Order with "Created" Status cannot be used directly to register Arrivals because it's just registered working document not yet accepted by responsible person (e.g. by Purchase Manager). How long the Purchase Order will have "Created" Status depends from the number of open questions that should be agreed with Supplier.
In order to activate the possibility to register Arrivals of ordered goods, the whole Purchase Order or particular Order Lines should be Released (otherwise, they should be Cancelled). The corresponding "Release" options are included into Context Menu for the Purchase Order Header and for Order Lines. The Order Status and Order Line Statuses will be changed accordingly after calling options noted above.