The DDI Summary page lists all of your company's DDI's, their type and what they do at different times of the day.
If you select a number, you can choose:-
Which site it is part of
The Time Schedule to use for the number (which will allow day/night/timed routing of calls) - or set to ALWAYS to have it go to a pre-set destination.
The converted number (if it is a mobile it must have a 9 added to the start), which can be a scenario, group or extension.
You can add a remark to label the DDI if you require so you can see at a glance what the numbers are for.