For your first question:
0x171 and 0x19E are representations of hexadecimal values in C.
0x171 = 369 (decimal), 0x19E = 414 (decimal).
These values are chosen as 'limits' and if you look, you'll see there's a few of them used in the radar program, one for each possible led on the radar output display.
They are used as comparators for the IR sensor data input. Depending upon the value coming in, a different led may or may not light up on the display.
(I'm just giving a high level description of what's going on)
For your second question:
Unfortunately there is no one
magical book out there that you can buy to learn all this stuff. It is a cumulative learning process like most things. Here's my recommendation:
-Learn the basics of Digital Logic Design (and, or, not, xor...etc).
-Learn the basics of Programming C.
-Get a Microcontroller Development Board & Programmer Setup (these are available alllll over)
-Begin programming very simple programs & work your way up.
These two tutorials give an example of a microcontroller & programmer:
http://www.pyroelectro.com/tutorials/pi ... index.html
http://www.pyroelectro.com/tutorials/pr ... index.html
If you want specifics just give a reply, I can make some recommendations.