The nominal GDP would increase when either of the following happen:
1) You produce more stuff
2) Prices increase
The first of those two represents "real" growth, whereas the second is just an illusion of growth. So, if the Nominal GDP increases, it might just be that prices went up with no real growth (although it's possible that you did also produce some more stuff).
The better measure is "Real GDP", which only increases when you "produce more stuff" and won't increase based on price changes.
 
     
             
 
                     
                    