There is really only one thing you need to do to setup a scale from within AIMsi.  If you go to Maintenance > General Maintenance > Workstations then select the POS tab, and within that the Devices tab, you will see a field named 'Scale Port'.  This needs to be set to the serial port your scale is attached to.

When you create skus ("New Sku"), modify skus ("SA Maintenance"), create/modify non inventory categories ("Non Inventory Categories"), or create/modify non inventory sub categories ("Non Inventory Sub Categories"), you have the option to select a 'Scaleable' box which means that the item requires a scale reading when sold.  This is optional, as you may toggle the scale button during a sale in order to get a weight reading.