This song is in open G tuning. (GBD) I’ll take you through how to tune your strings to this from the previous lessons tuning (Open D) in the video.
The simplistic beauty of open tunings is that your open strings will always sound great with your fingerpicking. Once you know some common chord shapes in these tunings it would be great for you to start improvising your own melodies and patterns. Just remember if you get into trouble to go back to picking or strumming your open strings. You’ll be surprised with how easy it is.
The Larks Song has a simple travis picked pattern with some chord movement up and down the neck. It’s fun to play.