You're at Barnes Railway Bridge: trains from Platform 2 up the steps on this side of the bridge go towards Hounslow every 15 minutes (less frequently on Sundays). Go under the bridge and up the steps to Platform 1 for trains to Waterloo via Barnes, Putney and Clapham Junction; these also go every 15 minutes (less frequently on Sundays).
If you've just arrived by train, you should walk southbound (with the river on your right) towards White Hart Lane (Oar 7 is on the corner). If you wish, walking northbound (ie with the river on your left) along the Terrace (Oar 6 is next to the zebra crossing) and then turning right into Barnes High Street will take you back along the Trail – but you should be aware that the leaflet and the Oars are set out from the perspective of someone walking the Trail in the opposite direction.