1. If there is an order with more than one item in the cart, enable Split Shipment if you want to split the order into different shipments based on the number of items in the order.
2. On placing the order, the admin will get different Shipment ID’s for each item, however, the customer will get only one order number.
3. Basically, if there is “n” number of items in an order, then “n” different shipment ids will be generated.

For Example: Let’s place an order with multiple items in it.

We can see only one order ID is generated through it has multiple items in it.

Now, on Magento admin panel, Navigate to Sales > Orders locate the order ID created.

Click on View to view the details of the order. When we click on view it will redirect to the page with all detailed information related to that order will appear. Click on Shipments to view shipment related details.

Here we can see, as the order placed had three items in it, therefore, three shipment ids are generated. If we click on View it will provide the details of the individual item in that order.