Every forum has a unique live search system built in that will allow you to search for topics or posts quickly, and will allow you to see results as you type. You can locate the search bars in the top-right hand corner of a topics listing in a board on the forum, or in the top-right hand corner when viewing a topic.
To search for a specific topic, click into a board that you think may have the topic that you are looking for. Once you're on the topics page in a board, find the search bar located just above the Last Post column on the topics page. Click the search bar to activate it and then begin to type. You can type in either something that you think may have been in the title of the topic you are looking for, or you can search for key words that were used in posts of the topic that you are looking for. The search results will update automatically after each keystroke you make to show you the topics that contain the keywords you are looking for.
The same can be done within a topic itself as well. If you are wanting to look for a specific post in a topic, but don't want to go through all of the different pages to look for it, you can use the search bar found in the top-right hand corner of a topic, just below the Reply button if available. Simply begin to type the words you're searching for that the post contained and the topic will update automatically to show the posts that contained the keywords.
If you need to further fine tune your search, click the magnifying glass icon found to the right of the search bar for more filtering options. Otherwise if you conduct some searches and are not finding what you are looking for, it's possible that what you're searching for is in a different board or topic on the forum. You can use the Search button found in the menu bar at the top of the page to conduct a forum wide search and you may be able to find what you're looking for using the global search tools there.