How to 'add an item to a list' action /Rules Module

Hello Everyone.

what i want to do is this 
i have a page called ( report ) ( custom content type ) 
i want to add a field to this page that can hold unlimited list of text or numbers.
the reason is i want to make it so that every time a user access this page, his/her ID will be added to the list.

so later i can use the Rules to check when the same user access this page if his ID is in that list (i'd show him a msg for example ) 

so what i want to know is two things :
1) what is the data field that can hold many values and i can add to it later?

2) how to add a value to the field using Rules or to check if the field has a specific Value? Thank to the help of people in the community, i learned how to set a value to a field but how and ADD a value to a the field ( which i should learn how to make by the answer of question 1 ).