Artefacts while filling in faces I'm incredibly new to Blender, so I apologise if this question has a simple answer. 

I'm trying to select vertices and fill them in, but when I do the filled faces seem to overlap with another face.

Here's a screenshot of the problem.

Any idea where I'm going wrong? Any help is appreciated.
Select all the verts or edges that make up the hole and press the F key. Your hole will be filled in as long as all the verts or edges are part of the same mesh.