Hello Emma,
The receiving bin goes into the - when you invoice an item and you cannot fill the stock.
For example :
You write an invoice for 64 CR1061 for a customer, Method will do a transfer order from the receiving bin to the customer bin. In your inventory, you only have 32 of the item CR1061. This transaction puts you in the negative now for this product.
Since you only had 32 of that item, your bin is now at -32 showing that you have some backorders for this product.
As for the bins, Method creates a receiving bin for your items. When you get product from your vendor, you fill out your item receipt, you receive that product into the receiving bin for that item. Once in the receiving bin, you can use a transfer order to move that inventory around to whatever location you are placing it in.
The customer bin is used to track how much inventory you have sold. when you sell an item, that item goes into the customer bin
You can find more details about the bins in the warehouse user manual. You can find that here.
Hope this helps explain the bins or you.