You will want to go in order from first episode to last on both shows. There's an underlying plot in both shows (which is not apparent, at first) Listening out of order will kinda ruin it. I don't know if you can listen chronoligically on Fountain

So I would suggest using the youtube playlists:

The Magnus Archives:

https://youtube.com/playlist?list=PLSbuB1AyaJk8zTF3nE2KRxuixG_A5gBKJ

Old Gods of Apalachia season 1(the other seasons you can find on the same channel)

https://youtube.com/playlist?list=PLDNou9zgeAqN4XRuE7wc7iMW7o8m7JjpS