I have used RSLogix 500 but now I want to use RSLogix 5000 because I heard it has this cool feature where you can writing logic once and then you can reference to it whenever you have a similar case so you don’t need to write 1000’s of lines of code, this would save a lot of rungs in the program and a lot of time,

does any one have information about that, and what the name of the function would be
and just a little info about it

You are correct about the ability to write a single piece of code and use it multiple times but I belive you may be confused about Logix5000. It is the programming software for the Controllogix platform. It will not program SLC's or micro's. It is very powerful PLC but you can create a similar one piece code in 500 by using the subroutines.

The CLX5000 using multiple programs that have independent tags. This means that the tags are the same, but they can only be used within its own respective program. Therefore, you can copy a program which has multiple routines and tags, and then reuse it many times again through out your program.

I hope this makes sense. Good luck.