F-43 and FB60 both are used to book an invoice for a vendor from FI perspective.
For eg, you want to book an invoice for a service rendered, we use this..
When we want the Inv to be routed from MM perspective, we do it thru MIRO....
Thru MIRO, we can have a ref to Purchase Req, Purchase Order, Goods Reciept and so on..
The same is not necessary and infact not possible when you do it thru F-43 or FB60.
Hope its clear for you now..