The society in Fahrenheit 451 is a futuristic projection of what might happen if some of our tendencies in society today continue on the path that they are on. For an explanation of how the society became the way it was, the best way is to look at Captain Beatty's explanation to Montag. When Beatty visits Montag, he explains that one reason books have been banned is because their society was too concerned with political correctness that they banned every offensive thing in a book. The problem was that something offended everyone, so getting rid of books altogether was much easier. Beatty explains,
"You must understand that our civilization is so vast that we can't have our minorities upset and stirred."
Secondly, people were just lazy. They didn't want to read an actual book, but the did want to be able to talk about books as if they had read them. So, what happened was that
"classics [were] cut to fit fifteen-minute radio shows, then cut again to fill a two-minute book column, winding up at last as a ten or twelve line dictionary resume."
Lastly, their society became the way it was because people did not want to actually do any deep thinking. Rather, they wanted to feel busy and productive without actually doing anyting. So, Beatty says that
"school is shortened, discipline relaxed, philosophies, histories, languages dropped...life is immediate, the job counts...why learn anything save pressing buttons, pulling switches, fitting nuts and bolts?"
The result of these three things is that their society is filled with people who do not know how to think for themselves, are entirely ignorant of their history, are fixated with entertainment, and don't even understand what true happiness is. That is the society that Montag lives in, and that he eventually learns to reject. I hope that those thoughts helped; good luck!