M = payment amount
P = principal, meaning the amount of money borrowed
J = effective interest rate. Note that this is usually not the annual interest rate; see below for an explanation.
N = total number of payments
Note the total number of payments N. The loan term may already specify this number, or you may need to calculate it yourself. For example, if the loan term is 5 years and you'll be paying in twelve monthly installments each year, your total number of payments will be N = 5 * 12 = 60