When you purse a house, you pay in arrears , or back pay on the house. For instance, your payment for August 1 pays for the month of July. Basically, the lender doesn't trust you to save up the money to pay taxes and insurance when they come due. This money is kept in an escrow account. When the tax and insurance bills come due, your lender pays them from this account.
Escrow accounts are negotiable.
Keep in mind that if you ask your agent to estimate how much house you can afford, they are aware of exactly how much house that translates to. If that agent starts to show you homes out of the range you feel comfortable with, let them know. With an experienced agent, you can sometimes do some creative financing to be able to qualify for a loan. Your agent won't recommend anything illegal, but he or she may be able to make suggestions about how to lower your monthly debts or how to finance your loan. Just be careful not to get in over your head.