Click the drop-down arrow in the "Nudge Value" menu.
Select the "Nudge Value" category of your choice. You can set it to bars and beats, minutes and seconds, or samples. Select the actual nudge value. For example, if the nudge value category is set to bars and beats, you might select 1/16 note as the nudge value. Or, if the nudge value category is set to minutes and seconds, you might select 1/4 a second as the nudge value.
Choose the "Grabber" tool and select the region you wish to nudge.
Press the "+" key to nudge the region forward or press the "-" key to nudge the region backward by the specified nudge value.