I think I should learn how to play d4. (1) what is the best way to learn? (2) as black how do I answer d4? Is there a book that deals with both? Stwils

I think every chess player should regularly play through master games, say the recent top level tournaments. If you do, then you have some idea already of what a typical d4 game looks like (e.g., white often plays 2.c4).

So, the same as with any other opening: just start a 1.d4 game and play your best, see what happens. After the game, lookup how the theory goes and where you could have improved (should do that after each game anyway, not just for the opening).

A good book that deals with all the openings is Fundamental Chess Openings.

i dont know how u guys study chess or play chess. but me when i play i just make move's and knowing that i have other moves thats adapting to where im going to go. I will certainly criss cross and take time's to dewll on some pieces and eventully when my opponent least expect's that's when i go for the throat. and the games ends in my  field. and very secretive that i have beaten some good player's

The best way to learn is just to study games that have already played out those openings and defenses. (esp tournaments). You should check a game database, like chessgames.com, where you can look at an opening and study all of the variations to defend against it. Here's a good example:

http://www.chessgames.com/perl/chessgame?gid=1479588

There are plenty of ways to learn, ( books at library and play more.) I don't have any specific books to recommend.

to learn d4 try covering qween gambit exepted, qween gambit declined, slav def and finaly the Nimzo-Indian Defense. then move on to the learning the kings indian wich totaly avoids the batle in the center, instead having a modorn aproch- black letting white achive a center in order to put presure on it

as for responding to d4, i enjoy the king's indian defense myself ... my favorite writers on the KID are Drazen Marovic and Joe Gallagher

as for your general query, indeed you should learn how to play d4 ... first it's a great surprise against an opponent that knows you ... also it broadens your understanding of chess in general ... and also it helps you to understand how to play black against d4 :)

Most d4 openings have certain ideas like important dark squared bishop and bad light squared bishop for Black,open c file,e5 outpost for the knight created by the d4 pawn,minority attack etc. Play some games where you will try to implement these ideas.After playing some games you will get the feel of d4 positions.

Before studying master games, you should atleast play some games on this opening first.