For full details on Delegate Access, see Microsoft’s website here. You and the delegate must use the same version of Outlook.
Keep In Mind
Before granting Delegate Access, it must be understood that Delegate Access and Calendar Permissions are two separate items that overlap with one another. Delegate Access allows you to act on another person’s behalf in relation to e-mail messagging and accepting, declining, or creating meetings; however, it must still interact with calendar permissions in order to do the latter. By default, granting meeting permissions alters the Calendar permissions for that person. However, if Calendar permissions are all that are needed, then one does not need Delegate Access to achieve this. One simply needs to grant the proper permissions to another for one’s calendar and then share that calendar with the desired account.