The first trick is activating the feature. It doesn't just automatically appear. You need to go here and opt-in to the beta for your YouTube account. Once you've done that, it is available in your YouTube channel.
To use it, go to the video you want to add the quiz to and click "edit".
After that, click on the "Questions" tab.
From there, it is pretty self explanatory. Just click, "add question" and you get this screen:
It's really that simple. Much easier than adding several Annotations to make your own quiz feature. There aren't many options to make the questions more appealing. But, I'm guessing they may add that in later.
Now, for the analytics...
Remember, this is in beta, so I didn't expect it to be perfect yet. With Annotations, the analytics tell you which annotations were clicked, by how many people, etc. With the quizzing analytics, at the moment, it just tells you if an answer was chosen or if the user closed the video. Not much detail at the moment.
Also, another limitation over annotations is that your can not jump to different videos or a different part of the video based on the viewers answer. If they answer incorrectly, they are prompted with a hint and the video remains paused. If they click correctly, the video just starts playing again.
I like the promise of this feature, but since it is still in beta, it doesn't have a lot of functionality yet.
Here is the video I added the quiz to if you want to see how the quiz looks and operates. The quiz is 23 seconds in:
Please note this is just a simple practice quiz and not intended to be something identical to what I would use with my students.