if you use "SQL Server Business Intelligence Development Studio" not "Report Builder" then on reporting services (where is you table):
- click View -> Properties Window (or just press F4)
- select the tablix
- on properties window find "General" and in the "DataSetName" choose your "Dataset"
- On tablix fields set values from your "DataSets"
Or just do like here(from 8:50): http://www.youtube.com/watch?v=HM_dquiikBA