Part kits behave the same on a Purchase Order as a normal part. You add the part kit to the PO the same as a normal part, and they display just like a normal part. The individual parts in the kit do not show on the PO (except POs created using the ADI integration).
When the PO is received, the kit is received into inventory, and the quantity of the kit on hand goes up. Nothing happens to the quantity on hand of the parts that make up the kit.
At this point, you have two new actions you can do with kits that you can't do with other parts. You can 'Build Part Kit' and 'Break out part kit'. If you select to build a part kit, the system will auto reduce the quantity on hand of the parts that make up the kit, and auto increase the quantity on hand of the kit itself. If you select to break out the part kit, it will do the opposite and reduce the quantity on hand of the part kit, and increase the quantity on hand of the parts in the kit. You can build and break out part kits anytime.
When you issue parts to a work order, if you issue the kit, only the kit will show on the work order. If you want the individual parts to show on the work order, then you should not issue the kit, but instead issue each part individually.