Hi Josla,
Firstly, congratulations on the new job! My first role on the railway was as a CSA (5 years ago), I've had a few since and can say with sincerity that it is still my favourite job I have done.
On your first day I would expect that you will be given your staff ID from reception, which will enable you to get into the staff only areas etc..
I would expect maybe a team huddle at the start of the shift where the Station Shift Manager will give you a run down of any goings on in the station and priorities for the day and you will be given a list of assistance jobs and security patrols designated to various members of staff.
As a new starter you may be 'buddied' up with a more experienced colleague at this point who will show you around the station so you can get your bearings and go into some detail about what is expected in your daily routine. I'm not sure whether you'll be doing security or mobility, but you may already know this, or I would expect that you will be told on the first day.
You'll have a lot of new names to learn and don't be offended if most people forget yours at the beginning! My big pieces of advice are get to know your colleagues and surroundings, do everything with a smile (things will be tough at times!) and most of all make sure you wear comfy yet smart shoes/boots!!
Any further questions send me a message and all the very best with it.