and 
enable you to move the highlighted row up or down in the sort order within the allowed range.
The Sort Order tab is only available on the few reports that can support a user specified sorting. Table of report default sorting orders
Do not confuse sorting with selections. Selection criteria have nothing to do with sorting.
The Order and Column Name columns show what the current sort order is for the report.
The Allowed columns show what the minimum and maximum allowed positions are for that particular column name. Due to the structure of some reports, sorts on some data must always precede or follow others. The Lo and Hi values tell you the lowest and highest sort order values allowed for that particular Column Name.
The and enable you to move the highlighted row up or down in the sort order within the allowed range.
The Restore Default button refreshes the block with the default sort order defined for this report.
See also:
Report format and output specification
Report dataset specification
Report format modification parameters
Recall of recent reports