If there is a tick in front of "exact match", the search is based on the principle of "concordance", i.e. the search system finds exactly the words you typed in all of the Bible verses (if you select "everywhere").
If there is no tick in front of "exact match", the "search" through the Bible shows exactly the words you typed + similar words throughout the Bible. This helps you to find what you need if you don't remember the exact word or words.
You can also choose what book to search in, or search only in the New Testament or in the Old Testament.