Datasets are like mini databases which allow you to load data into editable text fields on templates. Normally you would load either User data, Department data or Address data, but where you want to load other data you can use Datasets.
An example of this is where you want to allow users to choose a label (Tel, Fax or Email) by a drop down. You can make a little Dataset with those three values.
Then add a dataloader which uses this dataset
Make sure that your text object is set to load this data
Finally – heres what it can look like for the End User.