In the world of Nimble we have introduced a new construct called a FOLDER. This is designed to allow you to group volumes together by use case/customer/application, or to provision a logical allocation of storage for VVOL or SMI-S deployments. The Folder is what is recognised as a Container within VMware.
To create a folder head to Manage->Storage Pools, change to the Folder view and then create a Folder. You can specify a maximum size the Folder can use within the overall storage pool, and you'll want to check the VVOL checkbox. From there, rescan the VASA Provider within the Web Client and you should be good to go.
I'll create a blog post on this when i get some spare time....
Nick's nailed the answer here, and I just want to add a small bit of color.
I find that using the "New Folder" button from directly within Manage -> Volumes to be a bit easier to get to:
When you click the button, you'll be presented with the new folder wizard.
A couple of things about the wizard. First, you'll need to select the management type of "VMware virtual volumes (VVols)". Next, you'll select the vCenter instance. The "managed by" dropdown menu is populated with all the instances with which you have previously registered the Nimble vCenter plugin. Lastly, selecting the VVol management type will require you to set a folder capacity limit.
Creating the first VVol folder on your system will automatically create the required protocol endpoint. The folder you just created will show up as a storage container in vCenter, and you can specify it when creating a new datastore of type VVol.