A nutrition label is a document, and like any document it has conventions. Almost everything confusing about one comes from reading a part of it as though it were answering a question it was not written to answer.
Three things are worth separating before anything else: the reference quantity at the top, the list of components below it, and the ingredient list, which is a different document entirely and follows a different rule.
The reference quantity governs everything below it
Every figure in the panel is expressed against the reference quantity stated at the top, whether that is a stated serving or a fixed weight or volume. Change the reference and every number underneath changes with it. Comparing two packages without first checking that their reference quantities agree is the single most common way to misread a label.
Fixed-weight references exist precisely because they make comparison possible. Where a label offers both a per-serving and a per-hundred column, the second is the one built for comparing.
The ingredient list follows one rule
The ingredient list is ordered by weight, from most to least, at the point the product was made. That is the whole rule, and a surprising amount can be read from it. Where something appears in the sequence tells you roughly how much of the product it accounts for, without any figure being printed.
It is worth reading the list as a list rather than scanning it for particular words. The order is the information.
What the panel cannot tell you
A label describes a product as manufactured. It knows nothing about how the food is prepared afterwards, what it is eaten with, or how much of the package is actually used. Those are the parts of the question a panel was never designed to reach.
Treated as a product description, a label is clear and quite useful. Treated as advice about a meal, it will disappoint, because it is not that kind of document.