The traditional fixed rate mortgage is the most common type of loan program, where monthly principal and interest payments never change during the life of the loan. Fixed rate mortgages are available in terms ranging from 10 to 30 years and in most cases can be paid off at any time without penalty. This type of mortgage is structured, or "amortized" so that it will be completely paid off by the end of the loan term.
Even though you have a fixed rate mortgage and your principal and interest payment amount won't change, what might change is what's required for property taxes and homeowners insurance. Most mortgage loans are established with an escrow account to pay your property taxes and homeowners insurance. So a portion of your monthly payment is set aside in the escrow account and given that property taxes and homeowners insurance tend to increase over time, your mortgage payment will be adjusted to ensure there's enough money in your escrow account to pay your property taxes and homeowners insurance when the bills come due.