You can keep track of your Customers and Suppliers. Fill in their data manually or import from Contacts.
Tap on Document's header (toolbar) when editing Document to select Supplier for Incoming document or Customer - for Outgoing.
Long tap or swipe left (exposing 'i' button) to access all transction of Customer or Supplier. Besides that you can view Reorts by Customers or by Supplier.
Free version allows you to use up to 10 Customers and 10 Suppliers. If your business requires more of them then you can buy a subscription to remove this limitation.