Can you please explain me what is the difference between Process builder's submit for approval and Approval processes? If a record is submitted through process builder, to whom it will be assigned for approval?
In Process Builder You submit record for Approval. You need to specify the name of Approval process to which you want to submit the record.
Approver and other details will be defined on Approval process.
Approval Process:: Salesforce approval process is an automated process your organization can use to approve records in Salesforce, An approval process is combination of steps for a record to be approved and person has to approve it each step.