Hi Sunil,
The determination of an approver depends on the business rule defined.
Rule can be like,
Standard fixed user,
Org manager or line manager,
Cost center manager,
category manager etc.,
PFB the link for the detailed guide of process controlled workflow.
note: Once you configure process controlled workflow and create documents, you'll not be able to revert the system back to application controlled workflow.
Regards,
Karthik Babu