ApexEnterprisePatternsServiceClassL.cls

public class ServiceClass {
    public void sampleMethod(String accountIdParent) {
          // Define the Unit of Work instance. 
          // Mention the objects in independent to dependent order.
          fflib_SObjectUnitOfWork uow = new fflib_SObjectUnitOfWork(new List<SObjectType> {   Account.SObjectType,
                                                                                              Contact.SObjectType,
                                                                                              AccountContactRelation.SObjectType});
          // Selector class
          AccountContactRelationSelector acsSelector = new AccountContactRelationSelector();

          AccountSelector accountSelect = new AccountSelector();
          List<Account> childSites = accountSelect.selectLocationsByParent(new Set<Id> {accountIdParent});

          for( Account acc : childSites) {
                // process records or call Domain class.
                  .....
                  // Register the record for DML. 
                  uow.registerNew(acc);
          }
        // To create new records
        uow.registerNew(record);
        uow.registerNew(records);
        // To create new records + lookup fields
        // uow.registerNew(SObject record, Schema.sObjectField lookupFieldAPIName, SObject relatedToParentRecord)
        uow.registerNew(accountContactRelation, AccountContactRelation.AccountId, accountRecord); 

        // To create relationships additionally
        // uow.registerRelationship(SObject record, Schema.sObjectField relatedToField, SObject relatedTo)
        uow.registerRelationship(accountContactRelation, AccountContactRelation.ContactId, contactRecord); 


        // To update existing records
        uow.registerDirty(record);
        uow.registerDirty(records);

        // To delete the records
        uow.registerDeleted(records);

      // Call the commitWork() to make the DML operation. Unless calling this method, DML wont happen. 
      // Make sure that this uow.commitWork() only once in the transaction. 
      uow.commitWork();
    }
}