Contrary to what some buyers think, it's not calling your agent to see a home. It's calling a lender to find out how much you qualify for and then ask the lender to pre-approve you. Pre-approved means that not only have you spoken to a lender, but you've also completed a loan application, sent paycheck stubs, tax returns, bank statements, etc. to the lender. You may not need to send all of this documentation, depending on the bank/lender, but for the most part, the lender will want to see some verification of your finances. He/she will also run all of your information through software called Desktop Underwriting and within a day or two, you'll have a pre-approval letter. Now, you're ready to get out there with your agent and begin looking at homes.
Incidentally, more and more sellers are requiring that the buyer's agent send the seller's agent a copy of the pre-approval letter before a tour is even scheduled. So, don't wait on this very important first step. For years now, I've recommended that my buyers in the DC Metro area contact Bill Rozek with Embrace Home Loans at 301-325-6399 or https://www.embracehomeloans.com/location/maryland/rockville/bill-rozek. He's very responsive and gets the job done each and every time.