It means that your next check will have larger amount. The amount increased in your salary will be multiplied by 16 and added to your normal monthly salary. It means you will get the raised money for the 16 months all at once.
You need to know the percentage of the increase. Then multiply that percent by the salary that you were getting. Take that amount and multiply it by however many paychecks you have gotten in the time period since the raise. That is how much extra should be in your next check.