It is not that easy to explain the entire config.
However please refer to the post by Krishnakumar @:
Refer to blog by Federico @ to understand generic service use:
In most case, HCM P&F provided standard service like SAP_PA, SAP_PD would take care of saving data.
When there is some thing very specific where standard service can't cater to your requirement , you have the option of advanced generic services.
Chirs has a blog on this @: http://scn.sap.com/community/erp/hcm/blog/2012/08/20/hcm-processes-forms-when-all-else-failsadvanced-generic-services
For a single step process, data save can be configure at the process level.
And for multi step process save can be configure at the workflow level:
http://help.sap.com/erp_hcm_ias_2013_02/helpdata/en/4f/9c6c8bd1224b23e10000000a42189b/content.htm
SAP provided sample process is documented here:
Regards,
Sahir.