I use dual monitors at work, but have only one 24" monitor at home, which is enough for me.
For starters your graphics card has to be able to support this - not all do. Alternately you have to have two graphics cards - e.g. ATI Crossfire or Nvidia SLI set-up.
From there you right-click on your desktop background and choose "properties". Go to settings and advanced and find your GPU driver software..and from there it depends on the software and the graphics card.
It should be fairly intuitive if you have connected your two monitors properly - you would want the "extend desktop" option so that it considers the screen-acreage one large desktop. This allows you to move windows back and forth as per your needs.
Good luck with your set-up!