OK Jim, it was late and I was tired. Perhaps I should have made the effort and searched for a YouTube video that I didn't know existed. But I considered that more information from the requester was not unreasonable.

Anyway, to answer the question, it's arranged in A, and a simple way to accompany it would be
A |A |Bm |E |
A |A |Bm-E| A ||

or capoed up 2 frets

G |G |Am |D |
G |G |Am-D| G ||

Like Brian, I would categorize it as plain major/Ionian. Hope this is useful.