Depends on the format that they are in already. If you have a print, you can scan it and print a copy. If it's on a disk of some sort, you can do the same. If it's published online, you could make a print of that, but photographers sometimes put their logo over an online print, so that you can't always do that. If it's a colour slide, and you have a suitable printer, you can scan that and print it.
As per Buildersmate, unless you signed a very unusual contract with your wedding photographer you don't own the copyright on the photos and will not be allowed to make copies willy nilly.