Heat shrink tubing is a plastic tube of different diameters used to insulate electric wiring. You slip it into where you want to then use your heat gun to apply heat (could use a lighter if you are very careful and dont melt it) and it shrinks tightly over the spliced section.
Personally, I hate splices on my antenna and the only time it broke I just removed it from the receiver and soldered a new antenna wire. If you decide to do that make sure its EXACTLY the same lenght as the original wire.