From Online Manual
If you are looking for the search settings, see Search (admin)
The SMF default theme and its derivatives have a simple search field in the collapsible header as well as a search link in the main menu. Using the link in the main menu, users can also access the advanced search screen. Administrators can choose to disable search or regulate the search permissions for users.
The simple search field located at the top of the default SMF theme will, when viewing topics, filter search results to just that topic. The same applies to boards as well - when viewing a board the simple search field will filter the search to just results in that particular board.
While you can just type and search for any combination of characters, you should consider using modifiers to make the search really work for you.
The search tool searches the entire forum for any or all of what you specify that has been posted during the last 9999 days (which is more than 27 years)! To take more control of your search, you should use the advanced search feature.
Although the advanced search screen might initially seem a little intimidating if a forum has many boards and child boards, it is surprisingly straightforward when reduced to its basic components.*Despite initial appearances, there are really three options for how to search, with Match all words and Match any words being available from the drop-down menu, and Match as phrase also an option.*The default * in the By user field is essentially a wildcard matching any poster. Please note that, while you can replace this with any single username for a more specific search, it is not possible to search for posts by multiple users.*Show results as messages returns the full message containing the search string (with a reply option) instead of the usual linked excerpt, but will naturally result in much larger results pages which might be significant if you are searching for a popular word or phrase.
- Message age sets the minimum and maximum ages of posts to search.*Choose a board to search in provides you with another tool to narrow the scope of the search, with the default being 'all' (the whole forum or, more properly, all the boards to which you have read access). To search by board you need to expand the list of boards by clicking on Choose a board to search in, or search all and select which boards to search in and check the correct box.*The Search button not surprisingly sets the whole thing in motion, but pressing 'Enter' direct from any of the search fields is sometimes more convenient.
Using the simple or advanced search methods, you can still use search modifiers. These are powerful special characters which modify the way in which SMF handles your search string.
- Phrase search - use double quotes (") around your term ("search term") to search for the search term as a phrase instead of individual words.*Excluding terms - use a minus sign in front of terms you would like to exclude from the search result. For instance, "search -term" will search for "search" but not "term". The minus sign must have a space prior to it.
More search modifiers may be found at Google's help page. Not all of them may be useful in SMF at the present time.
See Search (admin) for options for the administrator to configure searching.