Probably the best thing is to download the datasheet:
http://atmel.com/dyn/resources/prod_documents/8271S.pdf
Most of the names are identical to what is in the datasheet. And things like:
_BV(WGM22)
means "the WGM22 bit".
So something like this:
TCCR2B = _BV(WGM22) | _BV(CS20)
Means: in the TCCR2B register (read the datasheet to see what it does) set the WGM22 and CS20 bits.