If you want to create your own customer group for your POS customers, you can do this in the Shopware backend under Settings → Basic settings → Shop settings → Customer groups by clicking the Add button.
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 product prices directly in the product details under Master data → Prices in the tab of the respective customer group. You can also easily use the free module Shopware Import/Export for this. These prices will then automatically be taken into account at the POS, provided the store customer is assigned to the corresponding customer group. If configured, any tiered prices will also be supported at the POS checkout.