You use the Assemblies selection to build or unbuild quantities of assembly items in inventory. Assembly items are created using the Bill of Materials tab in the Maintain Inventory Items window. In Maintain Inventory Items, you name and create the assembly. In Build/Unbuild Assemblies, you actually put together or "build" the assembly from its component inventory items. You can also take apart or "unbuild" assemblies here.
Building or unbuilding assemblies
Changing components in an assembly item