On the Apple Developer website it states:
To deliver an OS X app extension, it’s recommended that you submit your containing app to the App Store, but it’s not required.
However, to make a Today Extension from what I understand: I must create a Cocoa OS X application then add a "Today Extension" as a target. However, I do not want/need this main containing app. All I need is the extension.
So, how do I create an extension without a containing app? Even though technically I need to develop the containing app to create an extension target.
I think you are misreading this: what they are saying is that an OS X app extension may be distributed OUTSIDE the app store - if you continue reading, you will see the following:
If you distribute an OS X app extension outside of the Mac App Store, Gatekeeper prevents the extension from running until the user opens and approves the containing app. Further, if you code sign with a certificate other than your Developer ID, users must explicitly override Gatekeeper to open the containing app to make your extension available.
All extensions, at this writing, must be part of a container app and Apple devotes a large number of pages describing how, why, etc. My understanding (and work on extensions) is that all extensions must be part of a containing application. If there is a way to do so without the container app, Apple has not indicated it.