Pointers, Advance Code References, etc.

Projects Programming
5

I found C and C++ books in the central library. Now, I need to look for manipulating AVR constants in Arduino, etc.
Example:

MCUCR = _BV (BODS) | _BV (BODSE);
MCUCR = _BV (BODS);

What's the brown out detector on Arduino, and what does it do?