Approval Flows are set up and managed in the Approval Flows section within Admin. You will require Account Administrator access in order to set up an Approval Flow.
In the Approvers drop-down box, tick the names of the users you would like to be the approvers for each approval stage; you can select as many approvers as you require to share an Approval Flow stage.
Expenses requiring approval from a shared approval stage are sent to all the selected approvers sharing the stage, with only one approver having to approve the expenses; these will then either move to the next stage, or if there are no further approval stages, to Finance.