What should you do if you find an ancient relic or artifact?

Disclaimer; I’ve found no old relic of the past, this question just randomly came in my head.

Take a really easy scenario, like you find a pear of anguish from the seventeenth century at a flea market, or the hilt of a Viking sword in your backyard or something. Say the artifact you find, or piece of artifact is in good enough condition, what do you do with it?

Are you required by law to bring it in to a museum or some such place? What exactly do you do with it, where or to whom do you bring it, or are you even supposed to touch it? If not, who do you call? (I’m guessing in my examples, the objects might almost fall apart if you looked at them)

What to do with old historical relics that come into your possession? There has to be some rules about this, if what you find has historical value?