Bleeding Master Cylinder - '92 Limited discs ABS

Chilton's thrown me for a loop. I'm trying to bleed the master cylinder. They say to 'disconnect front brake pipe fitting' followed by the 'rear fitting'. I'm lost. Here's a picture and a couple questions concerning the pipe fitting. Please have a look.

http://files.automotiveforums.com/gallery/watermark.php?file=/500/300869Master_Cylinder-med.jpg

Why are doing this, first of all?

I had the rear brake line of for about a week and quite a bit of the fluid drained out. So I think I got air in the master cylinder.