The intro shows an average day of Turfing on trains
1) How they introduce themselves to their audience on Bart (and in the case of this film to the people watching it)
2) What it is they do namely “Turfing” (A.K.A taking up room on the floor) by providing a show on Bart through dancing and collecting any donations from the passengers as a way of living.
3) Show that they are able to sustain themselves by showing a little bit of what they earned from 3 hours of dancing.
The ending helps to revisit the Turfers showing what they do every day following their passion of dancing which is also their way of staying alive (literally as this is how they make their money to feed and cloth themselves).