It is easy. You can select one of the data colunm in your file for the one you want to display in the balloon. In the legend pane, just click the data set you imported, then do right click properties, then click on the balloon tab. You can select one of the field in your data as the one you want to use for the balloon (you can choose any data column you want. Just add an extra column for the balloon in your data file, or choose any column you may want in your data file...) There are 2 examples fields in my dataset "baloon" and "address"
In my example, the pushpin dataset name is qq and i have choosen the field balloon to be displayed (you can select more than one if needed)
Good luck