I have a notebook that is for a previous job and I don't need it anymore. Is there a way to delete an entire notebook? Please help.

I am not entirely sure but I think you need to do this;

a) close the notebook in OneNote
b) go to the folder where it is stored (if local and current versions it should be under Documents/OneNote Notebooks)
c) delete the notebook (or move it to a sub folder)

I don't think OneNote allows you to delete straight from it.

Exactly as BingoTed describes!