LinkedIn and Endorsement

I don’t understand the currency of endorsements on LinkedIn. What are they, and what do they mean, both to the people who give them and to the people who see them? I only ask because I’ve received endorsements from a number of people, almost none of whom I’ve ever provided services of any kind to. How do they know what my skillset is, let alone that said skillset is of high enough quality that they’d be confident enough to provide an endorsement in said skills? I just find the whole system puzzling.

Have anything to add to the conversation?