Here you can see a list of all available containers. You can manage the items in the list using the appropriate icon on the left side - edit (), delete () and export (). New web part containers can be created by using the New container link.
If there is a large amount of displayed containers, you can filter them by their Display name using the filter above the list.
More resources can be found at:
|•||Developer's Guide -> Development -> Web parts -> Web part containers -> Creating web part containers|