rocknbil posted a good overview. The title is displayed bold in the SERPs so the keywords used in the query will draw the eye if they are in there. THEN use the meta description (which is not known to be used for ranking) to incite the searcher to click on your listing.
Title is for search ranking and catching the searcher's eye.
Meta description is for inciting that searcher into clicking through to your site.
They both work together.