From the main table, you will be able to see all the DID numbers that is associated to your account and how the number is mapped internally.
The DID Inventory page will enable you to assign a DID number within your inventory to either an extension or call group like Hunt Group, Call Queueing, Auto Attendant and Input Code Prompt.
To assign a DID number to an extension, hunt group or auto attendant, please refer to this document -
Assigning an Incoming DID to a User