This question is related to our other question about relocation of our hot water heater. The current plan is to put the new water heater in the garage on the cement floor, so our concern is how to prepare the area where the new water heater will reside. So, initially, we may only paint the area under the tank. There's too much stuff in the garage to paint the whole floor all at once.
So this question results from the confluence of two projects. The garage floor as it is, is abysmal, so we want to make it better. It has not been painted. The cement must be several decades old. (The house was built in 1977, but the cement floor was added later. We believe that the area was initially a carport with crushed rock.)
I am having a difficult time thinking of how I could make the question more focused--probably because I don't know anything about painting cement. Web searches mostly return hype from vendors. I sincerely appreciate the help from those who don't mind assisting a confessed novice.