Please check https://help.sap.com/viewer/6b8255b03aa44628880b5b71c16ddb91/MDG91_SP02/en-US/ab671f57df261d62e10000000a44147b.html on how to Create and Configure Process Model for Custom Objects
Please check the link : https://help.sap.com/viewer/6b8255b03aa44628880b5b71c16ddb91/MDG91_SP02/en-US/ab671f57df261d62e10000000a44147b.html on how to Create and Configure Process Model for Custom Objects