From personal experience, it takes practise.
First you learn a couple of songs to get by, then you find you can learn lots.
Now comes the tricky bit. As you get older, you get a new song in your head - it pushes an older one out.
You can only have a good repertoire if you keep singing 'em, otherwise you get "Old Folkies Syndrome". You start a song only to find you've forgotten it after the first verse.
Good luck with the Summer Queen.