The “Target” is another way to glue the vertices together, here you have more control of the vertex position, as you will move one vertex over the other, the number beside the “Target” button specify the distance in pixels between the two vertices for they to be glued. So to use it just enable the “Target” button and move one vertice over the other.
As I said before our new mesh doesn't have all the faces connected, so if we select one vertex and move it there will be another one behind it
And if we move all of them we will end with as many vertices as the number of faces around it.
So we need to merge all those vertices together, I've selected all the vertices of the mesh and click the “Selected” button with the range of 0,1, because we want only glue together the overlapping vertices.
Once it is done we go to Element to see if it is only one whole mesh. When we select the mesh it appears as one, but if we hide it, using the “Hide” button in the Selection roll-up menu, we see that many faces are left behind, and we can not even select the vertices of those faces... don't know how this happened, but we will need to fix it.
So what I'm doing here is keep the one element mesh I've just hide, and delete those faces that were left behind, and them fill the holes on the mesh creating new faces. With the Element enabled we select all the faces them press the “Delete” button.