If you want to create your own customer group for your POS customers, this is possible in the Shopware backend under Configuration → Basic settings → Shop settings → Customer groups by clicking on Add entry.
If you want to set different prices for your POS customer group, you can either activate the Discount mode in the window for creating/editing customer groups or adjust the prices for individual items directly in the item details under Basic info → Prices in the tab for the respective customer group. You can also use the free Shopware Import/Export module for this. These prices are then automatically taken into account at the POS, provided that the customer is assigned to the appropriate customer group. If stored, any graduated prices are also supported at the POS checkout.