Background: Anyone who has a mortgage pays a certain amount towards principal (the loan amount) and a certain amount towards interest. Over the life of the mortgage, the interest amount can end up equalling or surpassing the principal amount. For instance, a $240,000 loan at a 30-year fixed rate of 5% means that you'd be paying $223,000 in interest on top of the $240,000 amount of the loan. Yes, $463,000, not including insurance and taxes. You can plug in your own numbers here: http://www.mortgagecalculator.org/
And banks are smart -- during the first few years of the mortgage, the payments are allocated mainly to interest and not principal. So a strategy of "hey, it's ok, I'll sell the house in a few years to avoid paying all that interest" won't work.
This is why I hate borrowing money, but it usually can't be avoided if you want to buy a house.
However, one way to grow equity in your house and at the same time reduce the amount you pay towards interest is to make occasional payments towards the principal. If you have an extra $1000 here and there, and your checking and savings accounts are adequately funded for a few months, it's a possibility. Call your lender and inquire if there's a pre-payment penalty (and make sure you don't work with anyone who imposes such penalties whenever you buy a house), and if not, look into making the payments online. My lender allows me to do this with no additional costs or fees. And each time I do it, I reduce the amount of interest I'll have to pay the lender -- which I love.