Someone has said to me that you can see the memory that each tag has, is this possible?
You certainly can - just double click the data-type that the tag is of, and its "definition", or make-up, is shown, together with the number of bytes of memory each tag will use.
(Note : This will not work for the "Atomic" data-types, BOOL, SINT, INT, DINT, and REAL. These are the "building blocks" that all tag types are made from).