Data types

Hi Experts,

While creating data types ,when I right click should i select insert elements or sub elements

ex:table fileds kunnr,matnr

I gave name to data types (dt_tables) data types for tables,now this will show up to the bottom like dt_table,now shall i right click and select insert elements afater that shall i slect insert sub elements or elements or rows,what is the difference

Please advise

Pooja