Lets suppose, you have a main warehouse, that is responsible to supply something to 3 stores that you have (Store1, Store2 and Store3) - So you have 4 warehouses (Main and Store1, Store2, Store3)
You cannot get low stocks in Stores, so you need a Safety Stock, let's suppose 50 pieces in each stock, so your safety stock is 150 pieces in any warehouse, when the safety level is below than Safety Stock (In all warehouses), it's start the reoder flow.
The Reorder Level, is a critical quantity that you assign for each warehouse, to they handle Material Requests automatically.
The Order Quantity is how many pieces will be ordered, on each Material Request (you can have 1000 as transfer from main to store*s and 3000 from Supplier to main)
The minimal order quantity is about SLAS (Service Level Agreement on Supply), when you have a agreement with the supplier, if you handle 3000 pieces him will delivery it to you in less than 72 hours, or something like.
You have reports for
Items Requested but not Transfered
Items Ordered but not Billed (Received)
And if you configure the reorder level, ERPNext will raise to you Material Requests automatically