Reading your follow-up comments, it sounds like you have Replenishment System set to Assembly, so the Manufacturing Policy field is ignored. Your Assembly Policy is what will matter here. You stated that you need to build the Items based on Orders, but that you also need to keep some stocked. This would mean you use the Assembly Policy set to Assemble-to-STOCK.
You would use a Reordering Policy of Lot-for-Lot, which allows for a Safety Stock Quantity. This allows you to maintain some stock level, but also build more when your demand (Sales Orders) is present. The Planning will often just be replenishing your Safety Stock level as you sell Items. In the case where you get a spike in demand, the system will pick up on the additional orders and account for them AND replenishing stock.
For comparison, the Assemble-to-Order policy would only create Assembly Orders when you enter the Sales Order Quantity. This policy is for build on demand without a stocking process, so I would not suggest this option.
Hopefully the Assemble-to-Stock policy with Reordering Policy of Lot-for-Lot and a Safety Stock Quantity meets your planning need. I would suggest using the Planning Worksheet for planning to get the suggestions on when to make more based on your current demand compared to your available supply.
P.S. If this suggestion was helpful in resolving your question, please mark it as a Verified Answer to help other forum Users.
Best Regards,
Ben Baxter
Accent Software Inc