I'm a MASSIVE noob to Maya, so please try to explain things simply if possible or include shortcuts for commands, that would be really appreciated, thanks.

I'm just starting to model and following a tutorial on how to model a head for my character.
I am using duplicate special and modelling half of the face etc.

I'm at a point in the tutorial where it tells me to smooth the mesh, but when I do, this happens:
https://puu.sh/5qXYq.jpg

The person in the tutorial doesn't have this issue and they never mentioned merging or combining the meshes in any way at all. I have tried merging them but I must be doing something wrong.

Can I fix this or have I messed the whole thing up?

Thanks a lot