You can assign one or more managers to an event, so they can edit the details, description, add tasks and activities and assign people as helpers.

Go to the Event edit button (upper right on the event page)

This opens up the Event Edit page, where you can add a manager.

Start typing a manager's name to be presented with a list of existing members. If the member is not present, you  need to first invite them (see Invite button at the top of the app). You'll want to invite them as "opted-in' by ticking the checkbox so they can be emailed when you add them as a manager. That's the only way they'll be able to log in and manage the event! :)

(You can also change the registration type to NONE if you don't need an RSVP for this event.)

Make sure you click "Save changes".

You'll be able to see the manager's name on the event page. 

The Manager will automatically be emailed (as long as you opted them in when you invited them, or if they are already an active member). They will also find they are able to edit the event, post messages about the event to the community, If any member posts a message to the wall, the Event Manager(s) will be notified, rather than the Community Manager, so it takes a load off your plate! Enjoy :)