Answer:
A tag is always a separate piece of paper/card/plastic which it attached to a product, often by means of a string or tie of some sort. You can generally pull or cut it off quite easily. Tags usually have prices on them. It is possible, but less usual, to use 'label' in this case.
A label is often more permanent, and has the name of the product on it - think of a label on a bottle of wine, for example. A label on a bottle, jar or can is stuck to the product by means of glue, and you would not normally remove this. In clothing, the label is sewn into the garment (usually at the back of the neck), and you wouldn't normally remove this, either.