You will need developer, fixer, water, tongs, towels, and a safe light in you dark room. It must be pitch black when safe light is off. I found out you can use orange LED halloween lights as a safe light. It is cheaper and you get more light than a small red darkroom bulb. The paper from the box will be a negative to make the positive put another piece of photo paper under the developed negative face to face. The negative must be on top. Use a piece of glass to press them together and turn the lights on for a few seconds. Make sure your extra photo paper is safe and covered or it will all develop black. Now develop the positive. It goes in the developer then water then fixer then water then air dry.
Look on any retrophotographic site or pick up and old photography book from a second hand book store to find the details of development and the chemicals. Ebay is a good source of cheap photography equipment too.
Good luck!
It's all done in a darkroom because, like film, the image initially imprinted onto the paper will be destroyed if left in direct light of any kind. There are filters used over dim lights to prevent that.
Other than that, the chemicals used and process is pretty much the same as developing film; developer, stop bath, fixer, and then a wash through some fresh water, to remove all the chemicals. If the wash isn't done, then the chemical stains will eat the photo.
Just research it. You need a lot of stuff, if you aren't taking a photography course in college, like I am. The darkroom and everything inside it is available to me, but an average Joe might have to make their spare bathroom into a darkroom, in order to be able to develop photos. ;)