By default, the system will list records that match or partially match each keyword you provide. So, searching for car security will list every company whose details contain the words car, carpenter, care, or security.
By selecting the Exact Phrase option, the search is limited to records which contain only a precise match for the entire set of keywords you supply. So, in the above example, this option would only list records that contained car security as a specific phrase.
The search engine is never case-sensitive.