s you see in book stores are published by pubishers
, who usually take your work, print it and distribute
it, and take their cut
Alternatively you can decide that you want your work to be self-published, at your own cost, so that you may keep all the profits. Of course this means that you will probably not get a very large distribution...
Basically you simply pay for a printer to print X copies of your work, and thats it, end of story! You now have to go and sell these books to stores or people. Hence the popularity of publishers! :)