I've recently started learning Blender and faced one problem.
After applying subdivision surface modifier I have plenty of extra faces.
I've watched some teaching videos and I suppose additional faces shouldn't be added.
Is it OK ? How to avoid this problem if it isn't.
I think you have some double vertices over there. shortcut W > remove doubles might solve your problem. Also try to keep faces as quads. Subdivision surface with triangles doesn't give optimal result.