A purchase order can be accepted a few ways.
If you navigate to your purchase order listing by clicking SCM - Purchase Order - Purchase Orders, go to your pending listing of purchase orders and check the box, select action at the top left -> Accept
The second way is to open up a Purchase Order to Edit, and create a bill, which will then tell you you need to accept the purchase order first and if you click yes it will accept the purchase order with also creating a bill
