Knowledge Base Help & Documentation:
How can I make a search after my migration to phpBB is completed?
phpBB provides 2 search systems for you to choose from: Fulltext Native and Fulltext MySQL.
Fulltext Native is included in phpBB core and is more flexible in terms of configuration. Fulltext MySQL makes use of mysql functions of fulltext search and doesn’t take much place in phpBB database.
To set a search – go to General tab -> Server Configuration -> Search Settings.