Bindings and stance settings

One of the first things you need to know about setting up bindings on a new board is "which way are you going to stand?"

On a snowboard you stand sideways and the foot you have in front determines if you are 'goofy' or 'regular'. left foot forward is called a "regular" stance, right foot forward is called "goofy" stance (I am told that this term comes from surfing).

There are several ways to tell how you should set up your board. first, put on some socks and run and slide across the kitchen floor. Take note of which foot is forward when you slide.
Another method is the "shove" method. To do this have a friend gently shove you from behind when you aren't expecting it. whichever foot naturally goes forward first in both these cases is probably the foot that should go forward on your snowboard.

Another, slightly more scientific method which I have recently heard is this. Find out which of your eyes is the dominant eye and put the other foot forward on the board. for instance, my right eye is my dominant eye, so I would put my left foot forward. (and I do! what a coincidence.)

How wide should the bindings be?

The official rule is "about shoulder width"...most everyone who is between 5'-5" and 6'-2" tall uses an 18-20" stance width. If you fall within this height range simply start at 20" and do a little experimenting to see what is most comfortable. because that's really what it all comes down to...does it feel natural for you?

What angles should I set my bindings to?

Binding angles are also purely a matter of personal taste. a fairly typical freeride setup would be 15 to 27 degrees in front and 6 to 18 degrees in the rear.

I personally run 21 front, 12 back for most of the season but, In the springtime when I ride mostly halfpipe I switch to 15 front and 6 rear.
I experimented with everything from 0f/0r all the way up to 30f/27r before finally deciding that these are the settings I like best.