Selkie means Seal in the Orcadian dialect of the Orkney islands in Scotland. They are sea creatures that seems to be interested in humans. Often seen by the shore lounging about while watching humans or even further into the sea, with their heads poking out of the water.
They look exactly like seals with an exception that they can turn into humans, very beautiful humans. To become human they would take off their seal skin as if taking off a costume. Then once they turn into humans, they would dance, play or bask under the moonlight or sun at outlying skerries and shores just like how most humans would do at the beach BUT they would all be naked.
The seal skins are their way of transforming back into seal form. They are bound forever in human form if the seal skin is lost in what ever way possible. Now, because they are beautiful creatures, there are a lot of stories where men and women alike were attracted to them.
For women, to make contact with a male selkie, during high tide, you need to shed seven tears into the sea. This works especially if you have an unsatisfying sex life. Then a male Selkie might just appear. And like most men, they would happily accept the offer.
For men, there is no specific way of calling them over. But most folklore about men and Selkies goes like this: man tricks selkie-girl into handing him the sealskin, man forces Selkie-girl to marry him with a condition of giving back the skin if they have a child together and would end with the man destroying the skin. Or the Selkie-girl somehow managed to obtain the skin through chance which of course led to revenge.
There are a few exceptions where the men doesn’t even know the wife is a Selkie until an event where the husband is drowning and the wife had to go save him by turning back into a seal.