Gunslinger?

Ok, I've been reading through King's novel "The gunslinger" further, and have come across an odd thought. What exactly is a gunslinger? Supposedly the main character (whose name hasn't been revealed yet, it is merely "gunslinger") is the last of his kind and comes from 'another world'. Some kind of fantasy world where everything has been destroyed. However, there isn't exactly a whole lot of technology involved in the book, as the character is using some old western 6 round pistols, and all the water found come from wells. So my question is, what is going on?!? I'm completely lost right now, as the storyline is becoming difficult to follow. Things keep jumping around from past tense to future tense to present tense, making the reader a little bit disoriented. I've given up as to attempting to figure out which time period the narrator is speaking of, and just trying to read through it. It's becoming pretty difficult to read more than 10 minutes at a time.