There are currently several thousand extensions listed on the Joomla! Extensions Directory, also known as the JED (http://extensions.joomla.org), so it would be very difficult, if not impossible, for one person to be familiar with all of them. As a result, we will need to take our time finding just the right extensions.
Luckily, the JED is divided into categories where we can view all the extensions related to that category or topic, and it can be searched along with the Internet in general, for extensions that we want. Alternatively, we can ask other people we know who might be more knowledgeable than ourselves.
The best way to use the JED search is via the advanced search feature, which can be found at the top of the page and to the right of the search box as shown:
When searching for extensions though, I actually recommend using Google over using the built-in search on the JED if possible, as at the time of writing, the search is not as useful...