aiyah i'm still not sleeping..
ok typically the number of valves depends on how many cylinders a
car has... so a 4 cylinder car can have either 12 or 16 valves,
which is 3 or 4 valves per cylinder.
for the 4 valve one, there'll be 2 for input (air) and 2 for output
(exhaust) the fuel comes from the injectors (for fuel injected
cars, of which most are nowadays)
for the 3 valve per cylinder, 1 will be for input, and 2 for
exhaust.. i THINK!! maybe it's the other way around.. can't
remember.
as for which is better i guess the 4 valve per cylinder one? why? i
have NO IDEA!! mauahhaha 
and yes.. as far as i know.. the cams control when these valves
open and close. 
