To communicate how a purchase order gets approval, flowcharts like this one can be useful because they show every step of the process. This one also employs the basic rules of visual grammar.
Text in this example:
Purchase Order is received
P.O. from existing customer
P.O. from new customer
Requestor is outside the US or Canada
Request other payment form
Submitted to Controller for Approval
Obtain Completed Credit Application
Outstanding Balance still due.
Purchase Order Approval Process