Truly Superior

Perhaps the number one thing to keep in mind about Narcissists is that they honestly, literally, fully believe that they are BETTER THAN YOU. As in categorically. They believe they are a superior KIND of human being, and you're NOT. You are not one of them, you're just not, and you never will be (in their minds).
Why do they talk to you, then?

Well you might be a relative, so they're "stuck" with you, but you can see their disdain by the way they don't invite you to things, or constantly criticize and correct you, or leave you out of conversations and decisions, or treat you like you're incompetent, unstable, or just not good enough.
They might have mistaken you for one of THEM when they first met you, so they wanted to hook up with you and rule the world (according to THEIR plans, of course).
They might see you as a way to improve their IMAGE by association with you.
They might want to own you, like a pet, or a slave.
They might be fixated on having sex with you.
They might only talk to you when there's no one else around.
They might want something you have, anything at all, from money, to your car, your house, your family, your career, your reputation, your "power" (if they think you have some). It could even be your dog, or your friends; who knows.
They might want to get into places and associate with people that you have access to.
They might want to be YOUR "sidekick", and for you to be their "protector", parent, caretaker, bodyguard, provider.

~(If a Narcissist is reading this post right now, their reaction will most likely be eye-rolling or some kind of invalidation like "Oh brother, who cares?!", or defensive justification of the behavior they recognize like "Everyone does that!" or "Some people really ARE 'losers'!", or they'll adamantly deny they do any of these things, or ever have even come close to doing any of them, and could never, ever, ever, and anyone who does do them is EVIL and should be burned at the stake, or completely insane and should be locked away forever (deflection/projection/extreme reaction/lack of objectivity or empathy).)