Can you help me find my keys?

I was lucky enough to join a session with a band called The Whiskey Dogs recentlyWhen I asked about the key in which a number of tracks on their CD were played in the reply was as follows:-"Keys Old Reuben is in A modal, Man of Constant Sorrow is in G modal, Old Joe Clark is in A, and Wayfaring Stranger is in Em. Not sure how dulcimer friendly they are but good luck"I have tried to get my head around this but I could do with some helpIs A modal the same as A Dorian ? And A , A Mixolidian?Is G modal G Ionian?Finally how do I tune to Em?Any help would be much appreciated!