have you seen any examples on C coded for AVR??? check the Datasheet!!!!!
SPE is a bit of the SPCR register... as in avr-gcc you can't access individual bits directly... they use the 'bit value' aproach...
some example:
say SU equals to 3 so we mean to turn on only the bit3
we want this REG = 0000 1000 , right?
00001000 binary equals to 8....
which is the relation between 8 and 3 ???? of course power_of_2 !!!!! 2^3 = 8
in binary, there is a more easy approach of power_of_2 ... it's called shifting...
so we shift one bit theree times...
we have 1 bit only:
0000 0001
... and shift it three times!
0000 0010
0000 0100
0000 1000
now we have the 3th bit activated!!!!
the shift operation in C is ..... << ....
so....
REG = 1<<SU ; from my lil' example...
in your case:
SPCR = (1<<SPE) | (1<<MSTR) | (1<<CPHA) | (1<<CPOL) | (1<<SPR0);
means: on the register SPCR, set the bits SPE, MSTR, CPHA, CPOL and SPR0 and clear the rest...
if you don't know wtf does each bit... you must read the datasheet troughfully....