Just quoting straight out of the book on page 79 (User Guide)
o Like: Includes only results that are close in spelling to the specified search terms.
o Fulltext: Includes only results that exactly match the specified search terms.
o Combine (Like and Fulltext): Includes both exact matches and close matches.
Most people use combine (make sure to reindex). Remember these search results won’t always be the best. Personally, I would suggest setting up Solr (which can be a whole project in itself).