'When The saints Go Marching In'. Every kid with a guitar learnt it in my day, in the 'hot' style, and I started playing it in the mid '50's as soon as I had my first guitar when I was ten. You only need to know four chords to play it - G, G7, C and D7 - all of which are probably the first chords 'would be' guitar players learn anyway. I got a little group together around that time in my home town of Swindon, and it was our 'go to' favorite. It's a gift of a song for anyone wanting to understand rhythm, strumming and foot tapping music. Also, all the people we played to seemed to know at least the first verse, and they would sing along - it has such joy in it. The second song I learnt was 'Oh My Darling Clementine'. After that, I dived into Rock and Roll and Country style songs and I was on my way.