Autopsy contains a keyword search ingest module that extracts and indexes strings from the files on the image being ingested. Search queries will not be executed until the ingest module has finished running.
To see keyword search results in real-time while ingest is running, add keyword lists using the Keyword Search Configuration Dialog and select the "Use during triage / ingest" check box. See (Ingest) for more information on refresh speeds and ingest in general.
Once ingest is finished and the index has been created, the Keyword Search Bar will be available for use.