Well, it could have been deleted (the icon not the app) or it could have been merged with another icon and made into a folder. So I would check for that first. When you tap any of the other icons, see if you get a little popup that shows more than one icon together in a folder. If you do get that, and it camera icon is in there, all you need to do is 'tap' and 'hold' the camera icon and then drag it out of the folder and put it back on the screen itself.
Now if it isn't in a folder with others, you can just 'tap' and 'hold' the background of your home screen and it should give you an overlay with icons, widgets, etc. Locate the camera icon and put it back on the home screen.