Someone dumb down Twitter for me

I hate twitter and have never used it, but starting a new site and figured I better!
How does messaging work?
If I see someone on Twitter I want to message, can I just message them directly? Or do I do @theirname? Or how does it work. I assume celebrities must get hundreds of messages a day, so there must be something that stops it, no? Or do they have to follow me in order to message?

Second, seems no one posts their email anymore only Twitter. So kinda ties in to the above, but how do I get in contact with them if they don't post email anymore, only their twitter?

DM is like a message right in their inbox, there is a limit and twitter sometimes doesn't allow links within the Direct Message, when you @ someone it's like starting a conversation, "hey @ben whats up?"

I don't understand what you mean on the second part

unfollow.me allows you to auto DM when somebody follows you you can also put your site link there i get 20-30 visits from twitter that way useful if you get couple of hundred followers everyday

Well the first reply didn't really know what he was talking about. He combined tweets with DMs. The second guy just skips what you're asking and just tries to introduce you to Twitter spam.

DMs can only be done when you both follow each other. Therefore celebrities don't get a lot of these, unless they follow a ton of people.

However, tweets mentions, found in the notification tabs are what celebrities get a lot of. However, if they have under 50k followers, then there's a decent chance they'll read it. Justin Bieber? Chances are no. I tweet people from Dragons Den and Shark Tanks and get responses and DMs.

The only one to contact is by tweeting them: "@JustinBieber DM me or email me at [email protected]"

^ Thanks man.
So if I did the @JB one you did, does everyone see that, or just him?
And will that be shown on my twitter account?

So if I wanted to get a hold of a journalist, that's the best way to do it?
It kinda sucks becasue they might think "Oh great someone that wants to sell something." And never email you.
WHere as if you had their email, you can send your full idea, and they'll atleast more or less read a sentence or two.