What you are looking for is referred to as consolidated picking.
The Inventory model group or warehouse is where you set this up to be activated.
What happens is that when posting a picking list the output order transaction is created. If these are not consolidated they will be posted to a picking route directly 1:1.
The output orders, when consolidated picking is done,are aggregated instead of posted directly to a route. Then you run the create shipment routine, the picking route with multiple output order lines from multiple orders are created based on some rules you have to set up.
Read more on this on technet.
[View:https://technet.microsoft.com/EN-US/library/aa571884.aspx]