When you Skip-A-Payment, you are taking the principal and interest you would have paid, effectively adding it to your outstanding mortgage balance.
A Skip-A-Payment will increase your mortgage balance. The length of your term will not be extended, however your amortization, or the time required to fully repay your mortgage in-full, will be slightly increased.
A Skip-A-Payment will not impact your credit score, and repayment will not be required until you pay your mortgage off.