An order minimum specifies the minimum dollar amount a brand is willing to sell to a retailer. If you do not reach the minimum requirement, then you will not be able to place your order. Brands also have the option to set a different minimums for first orders and reorders you place with them.
Please know the minimum is set by the brands themselves. You will notice that this amount varies depending on the specific brand.
As you add items to your cart while shopping for a brand, you will be shown whether you are meeting their minimum order amount or not. By adding more items to your cart, you will become closer to meeting this minimum.