@Raymond, your credit score will DEFINITELY impact your mortgage.
1) Underwriting - does the lender think you are a good risk to give you money? What's your history of repaying debt? Can you handle the monthly payments that you are trying to take on? So, the parts of your credit report like history of payment and outstanding debt have large impacts on whether they will even give you a mortgage at all.
2) Interest rates - the higher the credit score, the lower your rates. 720 is the base for good rates, 750 and up is even better.
3) PMI - I just wrote a long article on PMI. One of the things that affects how much you pay in PMI (if you don't have 20% down) is your credit score. So a low credit score, the higher the PMI.
If you have lower than 720 credit score, you aren't completely out of the mortgage game. But it does make it more expensive because interest rates go up. There are things like FHA loans that are available but they have their own issues - like never being able to get rid of their version of PMI. Like @ChiefMomOfficer said, pull your reports and see if you can get any items fixed. At least know what you are working with to see if it is even possible.
Bottom line - high credit score is good. The lower your credit score, the more down payment you'll want to lower your risk profile for the bank.