Two different types of services that Salesforce B2B Commerce APIs leverage are:

Logic services which are responsible for implementing business logic associated with entities. These services are defined inthe logic classes, such as ccrz.ccLogicCart, ccrz.ccLogicOrder, or ccrz.ccLogicProduct. Theseclasses provide methods for validating inputs, performing calculations, applying rules, or updating data for each entity.

Data services which are responsible forquerying and transforming data from entities. These services are defined in the service classes, such as ccrz.ccServiceCart, ccrz.ccServiceOrder, or ccrz.ccServiceProduct. These classes provide methods for creating, reading, updating, and deleting data foreach entity. Salesforce References: B2B Commerce and D2C Commerce Developer Guide, Service Classes, Logic Classes