Fixed rate mortgages are the most common type of mortgage. The interest rate remains the same for the life of the loan, so the principal and interest remain the same, too. With a fixed-rate mortgage, your monthly payment won't change (outside of property taxes, insurance premiums or homeowner's association fees).
Adjustable-rate mortgages, or ARMs, have monthly payments that can move up and down as interest rates change. Most have an initial fixed-rate period during which the borrower's rate doesn't change, followed by a longer period during which the rate changes at preset intervals. Generally, interest rates are lower than with fixed-rate mortgages, but they can rise, and you won't be able to predict future monthly payments.
FHA loans are mortgages insured by the Federal Housing Administration. Borrowers with FHA loans pay for mortgage insurance, which protects the lender from a loss if the borrower defaults on the loan. Because of that insurance, lenders can offer FHA loans at competitive interest rates and with more flexible requirements.
VA loans, or Veteran Affairs mortgages, don't always require a down payment and are available to veterans and active military members. VA loans are made through the private lenders but are guaranteed by the Department of Veterans Affairs, so they don't require mortgage insurance. Most members of the military, veterans, reservists and National Guard members are eligible after 90 days of service during war periods.