Hi Hegedus,
Tables can be referenced by their name. For example, if you open the Iris.jmp sample data file, you could reference it as: Data Table( "Iris.jmp" )
Current Data Table() will reference the last opened or used data table. Often it is useful to assign this to its own variable right away: dt = Current Data Table() especially if you will be switching between or opening multiple tables.
I hope this helps!
julian