The Policy-Based Data Structures (pbds) library in C++ offers commonly used data structures (like set, map, etc.) with additional features. It is a part of the C++ Standard Template Library (STL) and is provided by the GNU C++ Library. To use pbds, you need to include the necessary header files, such as for associative containers and for tree-based containers. To define a pbds container, you would use template parameters to specify the key, mapped value (in case of map), and the policy for the container. The policy specifies the type of underlying data structure to be used (like red-black tree, splay tree, etc.) and additional features like order statistics, hash functions, etc. Once the container is defined, you can use it like any other STL container, with the added functionalities provided by the policy-based data structures.