A Pre-approval is the first step that you should take if you are in the market for a property. Based upon the information that you give to a Mortgage Logic broker he/she will submit an application to a lender that best suits your needs and have them respond with a pre-approval that will guarantee an interest rate and mortgage amount for a certain period of time. A pre-approval essentially approves all aspects of you as the borrower with a financial institution. Once property aspects are known then this will be added to the pre-approval in order to obtain an approval.
Both pre-approvals and approvals done properly require that you provide verification of information provided. This would be verification of income, employment and property representations. Good effective realtors will require that you have a pre-approval before they start showing you property.