I finally got the skull where it should be more or less. Is it possible to add in some nostrils? What would be the best way to hollow out the space? Thanks.
There are many ways to do this. One way would be to just inset some faces and then extrude them towards inside.
You will probably want to edit the topology of your model using another modelling tools later to add more detail to the forms. That's why I would recommend watching some video tutorials about modelling.