You can read there about the (not so much known) DYNAMIC_SAMPLING_EST_CDN hint, the new Dynamic Sampling auto adjustment feature introduced in release 11.2 and other interesting details.
This time I highlight how to configure Dynamic Sampling - the first part focusing on the available session/statement levels. The next part will be posted soon and explains some other important concepts regarding Dynamic Sampling behaviour.
Unfortunately these topics are not covered very well by the official documentation. In fact the best coverage used to be in the documentation of the initial release that included Dynamic Sampling (9iR2). You can find the link to that old documentation version in the article over there.