In Replenishment, view bundles to see which finished goods need to be produced.
Select items and create a purchase order.
You will then be prompted to use bundle replenishment. When you are ordering components that will later be assembled into a finished product or bundle, select 'Use bundle replenishment' and click 'Replace Bundles'.
When you save your purchase order, you will then see the option to 'Create Assembly'.
Once your components are received, you can then create a new purchase order (or work order) to assemble components into the finished goods.