You goto a bank or loan company and fill out an application. They run a credit check. If you pass the credit check, they will want 2 or three years taxes/w2's and several months of your checking records.
They tell you how much of a loan you can get, and you have to decide how much you want to spend, and how much down payment you will have. If you go FHA you have to put down at least 3.5%, and for a conventional mortgage (non fha) usually 20%. After you get approved for the amount you want to spend you can talk to a realtor to see houses in your price range.