Assuming you are referring to a full tang knife: It is actually quite easy to put a knife handle together, as long as you have the correct tools and materials. First, start by inserting the blade into the pre-drilled holes in the handle scales (the two pieces that make up the handle). If the fit is too tight, you can enlarge the holes with a rat tail file. Once the blade is inserted, secure it in place by adding rivets. You will need a drill and bit that matches the size of your rivets, as well as a hammer and anvil (or something similar) to set them. To set the rivet, first, insert it into the hole so that half of it sticks out on each side of the blade. Place the anvil on top of one end of the rivet and then use your hammer to tap on the other end until it is flush with the surface of the handle scale. Repeat this process for each rivet until both handle scales are securely attached to the blade. And that's it! Your knife handle should now be assembled and ready to use.