World event serves to send data (variables, arrays,...) from one world to another.
Array is collection of elements of same or different type (depending on your needs) which you can sort, expand, extract from it, etc. For example you want to replay player movement you could append (add element to end of array) players current location to array each time player moves (or with loop). Then you will call recursive function or loop which will iterate trough each element of array (extract data from index position of an array in succession order 0, 1, 2,...) and teleport player to that location.