Hamlet: Act 1

After reading Act 1, I found that Hamlet is a lot easier to read than the other Shakespeare plays that I've read, though I don't find it quite as interesting just yet. It reminded me of "The Tell-Tale Heart" by Edgar Allan Poe, because everything seems dark and dreary in this Act.
I have a really hard time understanding who the characters are and how they're related/what their jobs are, like Marcellus and Horatio?
I believe this play would be considered magical realism because of the encounter with the ghost. The fact that no one seems too worried by the ghost freaks me out a bit, but also is a sign that maybe this is magical realism.
One of the first things I noticed was that the King seems like he's a dick, but maybe it's just how Shakespeare writes? When the King is giving his speech about his brothers death. He seems that he doesn't really care about him dying, especially when he says that he wants the town to celebrate with his marriage rather than focus on his brother dying. So selfish, he's making it all about himself. King Claudius and his wife also seem like they're forcing Hamlet to move on with the death rather than just letting him grieve, which kind of bugs me too. It seems like they aren't phased by the death at all, which also seems weird to me.
Also, how do Ophelia and Hamlet know each other? I hadn't seem any encounter (or maybe I missed it somewhere) with them and then she's talking about him loving her?
I do like how the different scenes skip back and forth from different characters, but sometimes that can make it a bit confusing.
One random question to finish up: Can everyone see the ghost of the King, or can only a select few see it?