So I am new to using the trains and the journey I'm going on requires 1 change at Clapham junction, and I was wondering how its supposed to go. I'm not sure what platform I will be dropped off at or which platform I need to go to (I will look up the platform information on the day after I buy a ticket at the desk) but it seems there will be around a 10 minute times gap for the interchange. I have no idea how big Clapham junction is, is this plenty of time to reach far away platforms? And how does the ticket system work for changing trains, will I just be able to get off at one platform and go to the other? Or do I have to show my ticket somewhere before I board the second train? The ticket is for one journey after all (and return), but I'm not sure if I can just jump off from one platform and then get on the other one. The journey I'm making is from Gatwick to Barnes, I also need to get back through the same/similar route. Any advise about interchanges or Clapham junction would be useful, thankyou.