The exam city intimation slip tells you which city your RRB exam centre is in, before the admit card comes.
It is released on your regional RRB website — log in with your registration number and date of birth to download it.
It is not the admit card: it does not carry the exact centre address, and you cannot enter the exam hall with it alone.
The full admit card with the centre address is released separately, a few days before the exam.
Check the slip early so you can plan travel and stay if your city is far.