Excel translation needed

[bwana devil]

i have the formula and want to know what it all means. the formula calculates a monthly payment on a loan. the formula is:

=PMT((C1*0.01)/12,C3*12,C2,0)

where
PMT = monthly payment
C1 = interest rate as a whole number
C2 = loan amount
C3 = length of loan in years

what does the first 12 and the 0 mean? also, i dont understand the english translation/logic of this formula.

original formula can be found here

thanks.