Mortgages come in a variety of shapes; some information applies to several types of mortgages. For that type of information, this is the place to start.
When I say many types, I mean there are government-backed mortgage programs and conventional mortgage programs and different lenders look at all these programs differently.
Most of the 1-4 unit mortgage loans are made with either FHA, VA, USDA or Fannie Mae or Freddie Mac in mind.
Those entities have their own rules, hundreds of pages, for what they want in a mortgage loans.
There are thousands of lenders that supply such loans; some of them add their own rules on top of those entities’ rules (overlays), some do not.
In addition, there’s a large number of mortgage loans that are made not to be sold to those entities, to be sold to private buyers or not to be sold at all.
For people with good credit, large down payments and good income, the best place to start is to go to the bank they have their checking and other accounts with and to a few other banks or credit unions. (You still need to shop around.)
For the rest, a mortgage brokerage or two should be thrown in the mix too.