How Stuff Works, has an amazingly in depth article on how Mortgages work.. The qualification process, debit to income, APR, payment, Freddie Mac, PMI, everything is covered. They also list ways to save money over the life of your mortgage. Plus they have charts.

From the article:

• Choose the right type of mortgage – A 30-year fixed-rate mortgage is the most expensive type of mortgage you can get — UNLESS you’re going to stay in your home for many years. Think about how long you will be in your home and choose the type of mortgage that makes the most sense and offers the lowest payments for the years you will be in the home.
• Make extra payments – Extra payments go directly to the principal of the loan. This means that the actual principal of the loan is knocked down by that extra amount you pay, rather than having the bulk of your mortgage payments paying interest. By doing this, you can cut your mortgage down tremendously. In fact, you can reduce your mortgage by almost 10 years simply by making one additional mortgage payment each year. Try out this calculator to see how much money extra payments can save.
• Bi-weekly payments – Just as making an extra payment will shorten the life of your loan, so will shifting your payment schedule to bi-weekly as opposed to monthly. What this schedule does is build in an extra payment each year without it “feeling” like an extra payment. Your mortgage payment can simply follow your paycheck schedule — if you get paid every two weeks, that is. With bi-weekly payments, a 30-year fixed mortgage will be paid off in about 23-and-a-half years.

The article is a few years old so the interest rates used as an example might seem off, and there is no mention of any recent developments in the mortgage and banking world. However, the core information in the article is solid and worth the read.