Datapool in rational robot is used to replace single or fixed value with multiple values in single recording instead of doing recording several times for different input datas.
U have to create a script by doing recording .
Select a field in the application for which u want to create a datapool.And goto the test manager Click the tools menu->manage->Datapools to create datapool follow the windows and enter the appropriate Datapool name,Field name its datatype .
And Enter the multiple values u want to replace in that field. Modify ur script by adding few statements in it saying about the datapool creation for the field in ur script.
And when u execute ur script u can c the application opening many times and the appropriate field is getting replaced with multiple values given by u.