The bands allow creating a headline and a lower half of a page for the lists output by the DataBand and GroupBands. The contents of a Header will be displayed in the beginning of a list output by a GroupBand or in a headline of every group. The contents of Footer will be displayed at the end of a list or a group.
DataBand and GroupBand can be used as containers for Header and Footers.
More information about using headers in GroupBand and DataBand.