Parameters define stock levels that trigger outputs. 

1) Navigate to MC Inventory - Inventory list - and click parameters 

Low Stock quantity: The quantity at which the item will display "low stock".

Low On-Order Quantity: The threshold amount on order that indicates a low resupply. 

Lead Time from Order: Lead time in days for On order items to arrive

Min. Stock Level: The effective minimum that will impact stock allocation. 

Reorder level: The minimum amount that will be re-ordered from a supplier on a re-stock. 

You should ensure you configure your sales channel policy (Inventory ->Channel Sales Policy) to reflect these messages and accurately inform customers of stock status. 

2) You can fill these in individually, or use the export function in MC Inventory -> Data Exchange -> Warehouse Item Parameters -> Export 

3) If you have multiple warehouses, make sure to fill in the warehouse_id field to differentiate the different locations.