Within your partner tab in Office 365 you are able to manage tenancies on behalf of your clients. With this also comes the ability to do this via PowerShell as well but with limitations such as Exchange Online can’t be managed via this process, so to do this you need a seperate unlicensed admin account created to do this.
As you should all be familar with the web GUI I will discuss the required PowerShell commands to get started.
Once you have connected your service use the following cmdlet:
$tenID=(get-msolpartnercontract -domain customer.com).tenantId.guid
Then to get all users for example use:
get-msoluser -tenantID $tenID
all the other commands such as set-user are avaliable just ensure you include -tenantID $tenID to any commands!
ahandyblog 
Hi, you are right. i can use this with the most commands, but how does it work with new-mailbox?
i need to create a new shared mailbox but it is not working this way. any ideas?
To create shared mailboxes this is where the feature is limited in its abilities as you cannot administer Exchange using this. The only way I can suggest is you login to the tenancy via the delegated administration option and create yourself an Global admin account within that tenancy if you don’t already have one. Then you will have to connect to the Exchange PowerShell using the new account created to run the command to create a new shared mailbox.
Or unless the tenancy is running Exchange Hybrid then on premise you could create the shared mailbox and DirSync it to Office 365. But either way defeats the point of delegated administration.