Many of the Xilinx IP are free to use. You can start IP evaluation by installing the free version of Vivado (called WebPack Vivado).
Within Vivado you will find the Xilinx IP Catalog which shows available IP. When you click on IP in the catalog, a wizard is launched that helps you setup the IP. Also the wizard will reference a Xilinx document that describes the IP.
Finally, after IP has been setup, the IP wizard will give you templates that help you instantiate the IP into your design.
See the following document for details of using Xilinx IP.