As nouns: the general usage is this. Both display some information. A label tends to be affixed directly to an object. A tag is attached more loosely, like by some other object, like a string. Sofia's answer gives a good example of this. Now, you can also "give a person a label" which means you classify them somehow. Both are also verbs, but I won't discuss that now.

Label is a small piece of paper or other material attached to something to show who is the designer while tag show you how much the item costs, the price!