If working on the public Galaxy Main server at http://usegalaxy.or, then this function is the far left tool panel. Search by the tool name.
If working on a local/cluster Galaxy, the tool can be searched for (is part of the BedTools suite) then install into your server through the Tool Shed http://usegalaxy.org/toolshed
If working at some other Galaxy, then the owners of that instance decide which tools to include. A request to add this one could be made to them directly.
Please let us know if this does not help, Jen, Galaxy team