I like the site Dunes suggested on HUD. Ironically, I just sent that link, along with other educational materials to someone today. Ironically, after showing them some properties, they found a home in their own neighborhood, they happened upon a home going on the market next week. The guy agreed to sell it to them for far less than market price, providing they didn't use Realtors. The guys mom is a Realtor and will do the contract for them for free. I still sent them the information, as they need to know the steps necessary to protect themselves and make it all happen. I sent them to their possible purchase with a heartfelt hope it works out for them. They are a young family and really could just use a break.
You should contact your bank or credit union and get them to pre-approve you. The good news is that you are in control. No pressure, just gather the information. While they are making their determination, your mission should be learn, learn, learn! There are loan terms, real estate terms, and title terms that you don't want people spitting at you without some basis. It's okay to not "know everything" but you should give yourself the edge by understanding the process. You need to do this whether you use a Realtor or not. I tend to try to educate my buyers so they aren't constantly on the defense in information overload. Not all Realtors do that. It's your job to know.
Once you have an idea of what you qualify for, you need to ask your lender for a Good Faith Estimate. That is a sheet that will tell you all the charges to you for doing the loan. That is your power tool. With that, shop. Get a quote and request the same thing from several mortgage brokers and banks. It's a good idea to take what you find back to your bank. It doesn't hurt to give them a chance to beat your offers. This is a chunk of change that deserves your diligence. You'll be glad you were so smart!
I wish you all the best!