As I understood...simple.
Place a "2-PORT DATA ITEMS" from scrolling menu on the left that will represent your s-parameter data of your amplifier. Then load your s-parameter data file by browsing in this component by double-click.This data file can be either Touchstone , CITI file or ADS natural data format. After that do your s-parameter simulation.
If you didn't supply Noise Figure , Rn ( or normalized rn ) , you can not do noise figure simulation.
I hope , I haven't misunderstood..