It’s located in the top right hand corner of the top navigation bar identified by the magnifying glass
It works really well in finding one word or several.
If you want to know if a link has been posted already; or join in a topic; or add something to an existing topic/thread with a similar/new item, use the SEARCH TOOL to find similar posts.
Example - if you want to see what posts are about Dr. Ardis - the image below gives an idea of what would be found by the search. From there, you can look to see if a thread has already been created to add something.