It’s entirely up to how you want to handle the data; the system is designed and intended to be flexible and provide multiple ways to solve a problem. I strongly suggest you read our documentation - not everything can be answered in an introductory video series, but the docs cover all these topics in depth. You can learn all about input/output mappings here:
As mentioned (and described in the linked documentation), the variables defined with a form attached to a user task are automatically added to the global scope (doc reference here). Typically you only need to configure mappings if you need to do something additional with the data.
For your use case of adding multiple values in a single form, and wanting to collect/track/use those throughout the process, I would recommend looking into the FEEL context type, which are similar to JSON objects. For instance, maybe an output mapping with the FEEL expression =append(globalListVariableName, { price: priceFormVariable, product: productFormVariable, quantity: quantityFormVariable }), which I would expect to create a structure like:
[
{ price: 0, product: 'string', quantity: 0 },
{ price: 1, product: 'string1', quantity: 0 },
...
]
(Note: I have not tested this, but that’s how I would start approaching it.)