Why do I have duplicate Vertices?

I’m very new to modelling and 3D design, I did some back in college but it’s been a good few years since I’ve done anything since! I’ve started getting back into it recently and started out by making a very basic and unfinished version of the Moonlight Greatsword from the Dark Souls/Kings Fields series, I started with a cube, used sub-divide smooth a couple of times and then used the extrude tool to create the blade and part of the hilt, and then extruded out from the hilt create the pommel and guard, but for some reason I’ve got loads of vertices all sat on top of each other?

Here is a gif of if http://imgur.com/a/3DcqK if need be I can upload the .blend for others to take a look at? Any help would be really appreciated! Also I apologise if this has already been answered before

Why do I have duplicate Vertices?

They do not appear as if by magic. You created them.
You could have duplicated some mesh by accident
You could have started to extrude something, changed you mind but didn’t actually undo it
You need to take more care during modelling and if you create any duplicates then remove them

Because you are a newbie, we have been there and have done that LOL

It’s really the extrude tool that most times is responsible for that. You hit E to extrude, then you want to cancel that hit escape and it looks like thw extrude never happened. But the the Vertices are there on top of the old ones because these are created as soon as you hit E. If you have a quad with all four Vertices selected you should see this orange gradient along the edges to next vertices. If you don’t see these you most times have duplicates. To get rid of them just select all bei hitting A and then press W and select remove doubles.