There is a search function where you can search the forums for any words. This is advised to do if you are unsure if a topic you want to post has already been discussed. Just put your keywords into the search bar at the top right of the page, shown below;
This will open up a larger search box like this;
Now you have the ability to search for posts by a particular member and or go to advanced search, which gives you many more options such as searching a particular forum.