Orientation

I hope your company provides some kind of orientation.  By law, they are going to have to talk with you about sexual harassment and they'll probably give you information about 'diversity'.  They are also going to give you a bunch of tax forms and (I hope) medical insurance forms which will probably be baffling.  That's basic orientation.  

Orientation should also introduce you to the company, the products, the market and the people.  Companies that devote time to this end up with employees who have a consistent vision about what the company is trying to achieve and how they will succeed.  If your new company doesn't provide this information, be sure to spend a lot of time on the website to figure out this stuff.  And go back to the site often because your perspective and understanding will change as you learn more about the internals of the company.

You should also get some kind of orientation from your department or your boss.  Or at least a 'welcome' and an introduction to a buddy who will show you around the office and introduce you to other people.  If you don't get a buddy, ask your boss "Do you want me to bring questions directly to you or is there someone else I should ask?"   By the way, the boss's assistant or secretary is frequently the most wired-in person in the place.  You can start by asking him or her the questions you'd want to ask the boss, and you may get a better answer.

We know that different workplaces will have different cultures.  Some are going to be warm and friendly and you'll get invited to lunch the first days with your peers and meet a lot of people.  Other places are less outgoing. (Particularly if they are heavily engineering-oriented.  We engineers don't need all that human interaction.  I'll deal with that later.)  You'll have to be more proactive in places like that (unless of course you're an engineer and don't care.)  A good place to start is that sales organization.  Those friendly, gregarious guys and gals are always good for lunch or a beer. 

Take a look at this amazing orientation handbook from a game company named Valve.  They communicate their culture and their policies in an unambiguous message.